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\\if expression
\\elif expression
\\else
\\endif
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\n

\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

\n

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\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

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\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

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\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
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Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block.", "/versions/10/facts/0/label": "Client", "/versions/10/facts/1/label": "Case-sensitive spelling", "/versions/10/tables/0/title": "Spellings in this manual definition", "/versions/10/related/3/label": "psql command-line options and complete manual", "/versions/10/tables/0/columns/0/label": "Command", "/versions/10/tables/0/columns/1/label": "Documented suffix modifiers", "/versions/10/tables/0/rows/0/modifiers": "None listed in this signature", "/versions/10/tables/0/rows/1/modifiers": "None listed in this signature", "/versions/10/tables/0/rows/2/modifiers": "None listed in this signature", "/versions/10/tables/0/rows/3/modifiers": "None listed in this signature"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "3731ea2aea8d6207a71389bfcf1d772c5d38f0454cd522636a563aadac2c40e8"}, "comparison_data": {"modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "definition": "This group of commands implements nestable conditional blocks. 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After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer, EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "6bc5a2ad59a45dac61053f17cb85dc6a6d3d73cf2b911344c3471f21f2d9273d", "manual_language": "zh"}, "11": {"facts": [{"label": "\u5ba2\u6237\u7aef", "value": "psql 11.22"}, {"label": "\u533a\u5206\u5927\u5c0f\u5199\u7684\u5199\u6cd5", "value": "\\else"}], "tables": [{"key": "spellings", "rows": [{"command": {"url": "/wiki/psql/cmd-69-66/?v=11", "text": "\\if"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-69-66/?v=11", "text": "\\elif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-73-65/?v=11", "text": "\\else"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=11", "text": "\\endif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}], "title": "\u672c\u7248\u624b\u518c\u4e2d\u7684\u5199\u6cd5", "columns": [{"key": "command", "label": "\u547d\u4ee4"}, {"key": "modifiers", "label": "\u624b\u518c\u4e2d\u7684\u540e\u7f00\u4fee\u9970\u7b26"}]}], "command": "\\else", "related": [{"url": "/wiki/psql/cmd-69-66/?v=11", "label": "\\if"}, {"url": "/wiki/psql/cmd-65-6c-69-66/?v=11", "label": "\\elif"}, {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=11", "label": "\\endif"}, {"url": "/wiki/tool/psql/?v=11", "label": "psql \u547d\u4ee4\u884c\u9009\u9879\u53ca\u5b8c\u6574\u624b\u518c"}], "release": {"ref": "https://ftp.postgresql.org/pub/source/v11.22/postgresql-11.22.tar.bz2", "label": "11.22", "major": "11", "channel": "historical", "manifest": {"pdf": {"A4": {"url": "/files/documentation/pdf/11/postgresql-11-A4.pdf", "bytes": 13057499, "pages": 2732, "sha256": "41d75855e610d0d9b8802b87dc5b080bef8d7e91c7cf69401fbf8d3cf801b4b5", "built_at": "2026-09-26"}, "US": {"url": "/files/documentation/pdf/11/postgresql-11-US.pdf", "bytes": 12961189, "pages": 2883, "sha256": "6a8899ef36935a5b7ed2b436207564a567a4ef1eb1c2200195876b8de4d4fa30", "built_at": "2026-09-26"}}, "tree": "11", "index": "index.html", "major": "11", "pages": 1125, "release": "11.22", "source_url": "https://ftp.postgresql.org/pub/source/v11.22/postgresql-11.22.tar.bz2", "svg_assets": 0, "source_mode": "en HTML verified against the pinned official archive", "source_sha256": "2cb7c97d7a0d7278851bbc9c61f467b69c094c72b81740b751108e7892ebe1f0"}, "revision": "53315ddaf3b3f9e6669fd1edc096bbb2cd4a65ea3e836c89e542b43af9ba3a7f", "evidence_kind": "English manual and source declarations", "source_sha256": "2cb7c97d7a0d7278851bbc9c61f467b69c094c72b81740b751108e7892ebe1f0"}, "sources": [{"url": "https://pg.center/docs/11/app-psql.html#PSQL-METACOMMAND-IF", "file": "app-psql.html", "label": "11.22 English manual \u00b7 app-psql.html", "anchor": "PSQL-METACOMMAND-IF", "sha256": "32c4d489e91e59715de2f7c3264fcccab3dd1eca54673dbfeac61304b0c54d4d", "language": "en", "original_url": "/docs/11/app-psql.html#PSQL-METACOMMAND-IF"}], "sections": [], "modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "description": ["\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5 \\if \u5f00\u59cb\uff0c\u4ee5 \\endif \u7ed3\u675f\u3002\u4e2d\u95f4\u53ef\u4ee5\u5305\u542b\u4efb\u610f\u6570\u91cf\u7684 \\elif \u5b50\u53e5\uff0c\u540e\u9762\u8fd8\u53ef\u4ee5\u9009\u62e9\u8ddf\u968f\u4e00\u4e2a \\else \u5b50\u53e5\u3002\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u53ef\u4ee5\uff08\u901a\u5e38\u4e5f\u4f1a\uff09\u51fa\u73b0\u5728\u6784\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u3002"], "manual_html": "
\\if expression
\\elif expression
\\else
\\endif
\n

\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5\\if\u5f00\u59cb\uff0c\u4ee5\\endif\u7ed3\u675f\u3002\u4e2d\u95f4\u53ef\u4ee5\u5305\u542b\u4efb\u610f\u6570\u91cf\u7684\\elif\u5b50\u53e5\uff0c\u540e\u9762\u8fd8\u53ef\u4ee5\u9009\u62e9\u8ddf\u968f\u4e00\u4e2a\\else\u5b50\u53e5\u3002\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u53ef\u4ee5\uff08\u901a\u5e38\u4e5f\u4f1a\uff09\u51fa\u73b0\u5728\u6784\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u3002

\n

\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

\n

\u4e0e\u5176\u4ed6\u53cd\u659c\u6760\u547d\u4ee4\u53c2\u6570\u4e00\u6837\uff0c\\if \u6216 \\elif \u7684\u8868\u8fbe\u5f0f\u53c2\u6570\u5148\u8fdb\u884c\u53d8\u91cf\u63d2\u503c\u548c\u53cd\u5f15\u53f7\u5c55\u5f00\uff0c\u7136\u540e\u50cf\u5f00\u5173\u9009\u9879\u53d8\u91cf\u4e00\u6837\u6c42\u503c\u3002\u6709\u6548\u503c\u4e3a true\u3001false\u30011\u30010\u3001on\u3001off\u3001yes\u3001no \u7684\u4efb\u610f\u65e0\u6b67\u4e49\u3001\u4e0d\u533a\u5206\u5927\u5c0f\u5199\u7684\u5339\u914d\u3002\u4f8b\u5982 t\u3001T \u548c tR \u90fd\u4f1a\u89c6\u4e3a\u771f\u3002

\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

\u88ab\u8df3\u8fc7\u7684\u884c\u4ecd\u4f1a\u6b63\u5e38\u89e3\u6790\uff0c\u4ee5\u8bc6\u522b\u67e5\u8be2\u548c\u53cd\u659c\u7ebf\u547d\u4ee4\uff0c\u4f46\u67e5\u8be2\u4e0d\u4f1a\u53d1\u9001\u7ed9\u670d\u52a1\u5668\uff0c\u6761\u4ef6\u547d\u4ee4\uff08\\if\u3001\\elif\u3001\\else\u3001\\endif\uff09\u4ee5\u5916\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u4f1a\u88ab\u5ffd\u7565\u3002\u5bf9\u4e8e\u6761\u4ef6\u547d\u4ee4\uff0c\u53ea\u68c0\u67e5\u5d4c\u5957\u662f\u5426\u5408\u6cd5\u3002\u88ab\u8df3\u8fc7\u7684\u884c\u4e2d\u7684\u53d8\u91cf\u5f15\u7528\u4e0d\u4f1a\u5c55\u5f00\uff0c\u4e5f\u4e0d\u4f1a\u6267\u884c\u53cd\u5f15\u53f7\u6269\u5c55\u3002

\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

\u4e0b\u9762\u662f\u4e00\u4e2a\u793a\u4f8b\uff1a

\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
", "manual_path": "app-psql.html#PSQL-METACOMMAND-IF", "localization": {"status": "complete", "sources": [{"url": "/docs/11/app-psql.html", "method": "same-major semantic node", "sha256": "01339254dd1dc30d095af846d0b6a7c01f96338187a6fbb8cf45290d5941196b", "language": "zh", "matched_nodes": ["#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[113]/p[0]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[113]/p[3]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[113]/p[4]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[113]/p[5]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[113]/p[6]"]}], "language": "zh", "original_text": {"/versions/11/description/0": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block.", "/versions/11/facts/0/label": "Client", "/versions/11/facts/1/label": "Case-sensitive spelling", "/versions/11/tables/0/title": "Spellings in this manual definition", "/versions/11/related/3/label": "psql command-line options and complete manual", "/versions/11/tables/0/columns/0/label": "Command", "/versions/11/tables/0/columns/1/label": "Documented suffix modifiers", "/versions/11/tables/0/rows/0/modifiers": "None listed in this signature", "/versions/11/tables/0/rows/1/modifiers": "None listed in this signature", "/versions/11/tables/0/rows/2/modifiers": "None listed in this signature", "/versions/11/tables/0/rows/3/modifiers": "None listed in this signature"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "b48ddf44cca6d8deb7e4593655dc6843d888c463446405ed9bfa2e3a4bf21774"}, "comparison_data": {"modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "definition": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block. The \\if and \\elif commands read their argument(s) and evaluate them as a boolean expression. If the expression yields true then processing continues normally; otherwise, lines are skipped until a matching \\elif , \\else , or \\endif is reached. Once an \\if or \\elif test has succeeded, the arguments of later \\elif commands in the same block are not evaluated but are treated as false. Lines following an \\else are processed only if no earlier matching \\if or \\elif succeeded. The expression argument of an \\if or \\elif command is subject to variable interpolation and backquote expansion, just like any other backslash command argument. After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer, EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "6bc5a2ad59a45dac61053f17cb85dc6a6d3d73cf2b911344c3471f21f2d9273d", "manual_language": "zh"}, "12": {"facts": [{"label": "\u5ba2\u6237\u7aef", "value": "psql 12.22"}, {"label": "\u533a\u5206\u5927\u5c0f\u5199\u7684\u5199\u6cd5", "value": "\\else"}], "tables": [{"key": "spellings", "rows": [{"command": {"url": "/wiki/psql/cmd-69-66/?v=12", "text": "\\if"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-69-66/?v=12", "text": "\\elif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-73-65/?v=12", "text": "\\else"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=12", "text": "\\endif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}], "title": "\u672c\u7248\u624b\u518c\u4e2d\u7684\u5199\u6cd5", "columns": [{"key": "command", "label": "\u547d\u4ee4"}, {"key": "modifiers", "label": "\u624b\u518c\u4e2d\u7684\u540e\u7f00\u4fee\u9970\u7b26"}]}], "command": "\\else", "related": [{"url": "/wiki/psql/cmd-69-66/?v=12", "label": "\\if"}, {"url": "/wiki/psql/cmd-65-6c-69-66/?v=12", "label": "\\elif"}, {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=12", "label": "\\endif"}, {"url": "/wiki/tool/psql/?v=12", "label": "psql \u547d\u4ee4\u884c\u9009\u9879\u53ca\u5b8c\u6574\u624b\u518c"}], "release": {"ref": "https://ftp.postgresql.org/pub/source/v12.22/postgresql-12.22.tar.bz2", "label": "12.22", "major": "12", "channel": "historical", "manifest": {"pdf": {"A4": {"url": "/files/documentation/pdf/12/postgresql-12-A4.pdf", "bytes": 13424351, "pages": 2803, "sha256": "7422cf53fd1939e7a3d2925231a88b0330e468afa5393627cac0ff86158a0621", "built_at": "2026-09-26"}, "US": {"url": "/files/documentation/pdf/12/postgresql-12-US.pdf", "bytes": 13322565, "pages": 2958, "sha256": "51f3b04e72907fc38512685946223452ea65f84419c60c66241dfa3396035e77", "built_at": "2026-09-26"}}, "tree": "12", "index": "index.html", "major": "12", "pages": 1131, "release": "12.22", "source_url": "https://ftp.postgresql.org/pub/source/v12.22/postgresql-12.22.tar.bz2", "svg_assets": 2, "source_mode": "en HTML verified against the pinned official archive", "source_sha256": "8df3c0474782589d3c6f374b5133b1bd14d168086edbc13c6e72e67dd4527a3b"}, "revision": "7a827e97cbfacd7febff75f34443e2043e40723de5b6d8c9d81a9430b65a37e4", "evidence_kind": "English manual and source declarations", "source_sha256": "8df3c0474782589d3c6f374b5133b1bd14d168086edbc13c6e72e67dd4527a3b"}, "sources": [{"url": "https://pg.center/docs/12/app-psql.html#PSQL-METACOMMAND-IF", "file": "app-psql.html", "label": "12.22 English manual \u00b7 app-psql.html", "anchor": "PSQL-METACOMMAND-IF", "sha256": "a5cec5a456a98610e98d1f1959d96ce57c8413bb392f0f5d6720fc561bb63627", "language": "en", "original_url": "/docs/12/app-psql.html#PSQL-METACOMMAND-IF"}], "sections": [], "modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "description": ["\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5 \\if \u5f00\u59cb\uff0c\u4ee5 \\endif \u7ed3\u675f\u3002\u4e2d\u95f4\u53ef\u4ee5\u5305\u542b\u4efb\u610f\u6570\u91cf\u7684 \\elif \u5b50\u53e5\uff0c\u540e\u9762\u8fd8\u53ef\u4ee5\u9009\u62e9\u8ddf\u968f\u4e00\u4e2a \\else \u5b50\u53e5\u3002\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u53ef\u4ee5\uff08\u901a\u5e38\u4e5f\u4f1a\uff09\u51fa\u73b0\u5728\u6784\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u3002"], "manual_html": "
\\if expression
\\elif expression
\\else
\\endif
\n

\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5\\if\u5f00\u59cb\uff0c\u4ee5\\endif\u7ed3\u675f\u3002\u4e2d\u95f4\u53ef\u4ee5\u5305\u542b\u4efb\u610f\u6570\u91cf\u7684\\elif\u5b50\u53e5\uff0c\u540e\u9762\u8fd8\u53ef\u4ee5\u9009\u62e9\u8ddf\u968f\u4e00\u4e2a\\else\u5b50\u53e5\u3002\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u53ef\u4ee5\uff08\u901a\u5e38\u4e5f\u4f1a\uff09\u51fa\u73b0\u5728\u6784\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u3002

\n

\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

\n

\u4e0e\u5176\u4ed6\u53cd\u659c\u6760\u547d\u4ee4\u53c2\u6570\u4e00\u6837\uff0c\\if \u6216 \\elif \u7684\u8868\u8fbe\u5f0f\u53c2\u6570\u5148\u8fdb\u884c\u53d8\u91cf\u63d2\u503c\u548c\u53cd\u5f15\u53f7\u5c55\u5f00\uff0c\u7136\u540e\u50cf\u5f00\u5173\u9009\u9879\u53d8\u91cf\u4e00\u6837\u6c42\u503c\u3002\u6709\u6548\u503c\u4e3a true\u3001false\u30011\u30010\u3001on\u3001off\u3001yes\u3001no \u7684\u4efb\u610f\u65e0\u6b67\u4e49\u3001\u4e0d\u533a\u5206\u5927\u5c0f\u5199\u7684\u5339\u914d\u3002\u4f8b\u5982 t\u3001T \u548c tR \u90fd\u4f1a\u89c6\u4e3a\u771f\u3002

\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

\u88ab\u8df3\u8fc7\u7684\u884c\u4ecd\u4f1a\u6b63\u5e38\u89e3\u6790\uff0c\u4ee5\u8bc6\u522b\u67e5\u8be2\u548c\u53cd\u659c\u7ebf\u547d\u4ee4\uff0c\u4f46\u67e5\u8be2\u4e0d\u4f1a\u53d1\u9001\u7ed9\u670d\u52a1\u5668\uff0c\u6761\u4ef6\u547d\u4ee4\uff08\\if\u3001\\elif\u3001\\else\u3001\\endif\uff09\u4ee5\u5916\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u4f1a\u88ab\u5ffd\u7565\u3002\u5bf9\u4e8e\u6761\u4ef6\u547d\u4ee4\uff0c\u53ea\u68c0\u67e5\u5d4c\u5957\u662f\u5426\u5408\u6cd5\u3002\u88ab\u8df3\u8fc7\u7684\u884c\u4e2d\u7684\u53d8\u91cf\u5f15\u7528\u4e0d\u4f1a\u5c55\u5f00\uff0c\u4e5f\u4e0d\u4f1a\u6267\u884c\u53cd\u5f15\u53f7\u6269\u5c55\u3002

\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

\u4e0b\u9762\u662f\u4e00\u4e2a\u793a\u4f8b\uff1a

\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
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-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
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A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block. The \\if and \\elif commands read their argument(s) and evaluate them as a boolean expression. If the expression yields true then processing continues normally; otherwise, lines are skipped until a matching \\elif , \\else , or \\endif is reached. Once an \\if or \\elif test has succeeded, the arguments of later \\elif commands in the same block are not evaluated but are treated as false. Lines following an \\else are processed only if no earlier matching \\if or \\elif succeeded. The expression argument of an \\if or \\elif command is subject to variable interpolation and backquote expansion, just like any other backslash command argument. After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer, EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "6bc5a2ad59a45dac61053f17cb85dc6a6d3d73cf2b911344c3471f21f2d9273d", "manual_language": "zh"}, "14": {"facts": [{"label": "\u5ba2\u6237\u7aef", "value": "psql 14.24"}, {"label": "\u533a\u5206\u5927\u5c0f\u5199\u7684\u5199\u6cd5", "value": "\\else"}], "tables": [{"key": "spellings", "rows": [{"command": {"url": "/wiki/psql/cmd-69-66/?v=14", "text": "\\if"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-69-66/?v=14", "text": "\\elif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-73-65/?v=14", "text": "\\else"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=14", "text": "\\endif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}], "title": "\u672c\u7248\u624b\u518c\u4e2d\u7684\u5199\u6cd5", "columns": [{"key": "command", "label": "\u547d\u4ee4"}, {"key": "modifiers", "label": "\u624b\u518c\u4e2d\u7684\u540e\u7f00\u4fee\u9970\u7b26"}]}], "command": "\\else", "related": [{"url": "/wiki/psql/cmd-69-66/?v=14", "label": "\\if"}, {"url": "/wiki/psql/cmd-65-6c-69-66/?v=14", "label": "\\elif"}, {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=14", "label": "\\endif"}, {"url": "/wiki/tool/psql/?v=14", "label": "psql \u547d\u4ee4\u884c\u9009\u9879\u53ca\u5b8c\u6574\u624b\u518c"}], "release": {"ref": "https://ftp.postgresql.org/pub/source/v14.24/postgresql-14.24.tar.bz2", "label": "14.24", "major": "14", "channel": "stable", "manifest": {"pdf": {"A4": {"url": "/files/documentation/pdf/14/postgresql-14-A4.pdf", "bytes": 14354704, "pages": 2944, "sha256": "8bc6b9dd7b246888bb77f0a5e8c39a2eae52e9926569832669c7d1600becb27c", "built_at": "2026-09-26"}, "US": {"url": "/files/documentation/pdf/14/postgresql-14-US.pdf", "bytes": 14242178, "pages": 3102, "sha256": "b7ecb5a5f62d8b9f73a69e25a7d26ba285373bc53168a553bff7b77955506db4", "built_at": "2026-09-26"}}, "tree": "14", "index": "index.html", "major": "14", "pages": 1158, "release": "14.24", "source_url": "https://ftp.postgresql.org/pub/source/v14.24/postgresql-14.24.tar.bz2", "svg_assets": 3, "source_mode": "en HTML verified against the pinned official archive", "source_sha256": "a7fa7ed3d558172355f51406097a7bd4f6b473be80f311ef7cda96bf383d8897"}, "revision": "588700d46356d8837c77c7c0a4e71e645fe6535983b8f1830aa8f2e4e41c40ae", "evidence_kind": "English manual and source declarations", "source_sha256": "a7fa7ed3d558172355f51406097a7bd4f6b473be80f311ef7cda96bf383d8897"}, "sources": [{"url": "https://pg.center/docs/14/app-psql.html#PSQL-METACOMMAND-IF", "file": "app-psql.html", "label": "14.24 English manual \u00b7 app-psql.html", "anchor": "PSQL-METACOMMAND-IF", "sha256": "8da20abaee171c53c05658cfb2580dea645070f40bad6b46a845d710ad74c3ae", "language": "en", "original_url": "/docs/14/app-psql.html#PSQL-METACOMMAND-IF"}], "sections": [], "modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "description": ["\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5 \\if \u5f00\u59cb\uff0c\u5e76\u4ee5 \\endif \u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684 \\elif \u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a \\else \u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002"], "manual_html": "
\\if expression
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\n

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\n

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\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

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\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

\u4e0b\u9762\u662f\u4e00\u4e2a\u793a\u4f8b\uff1a

\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
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Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block.", "/versions/14/facts/0/label": "Client", "/versions/14/facts/1/label": "Case-sensitive spelling", "/versions/14/tables/0/title": "Spellings in this manual definition", "/versions/14/related/3/label": "psql command-line options and complete manual", "/versions/14/tables/0/columns/0/label": "Command", "/versions/14/tables/0/columns/1/label": "Documented suffix modifiers", "/versions/14/tables/0/rows/0/modifiers": "None listed in this signature", "/versions/14/tables/0/rows/1/modifiers": "None listed in this signature", "/versions/14/tables/0/rows/2/modifiers": "None listed in this signature", "/versions/14/tables/0/rows/3/modifiers": "None listed in this signature"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "ae339b2fd868563f04bc2c4c5470eaa2ae6594923ea82e2f2055ddc348de961b"}, "comparison_data": {"modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "definition": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block. The \\if and \\elif commands read their argument(s) and evaluate them as a Boolean expression. If the expression yields true then processing continues normally; otherwise, lines are skipped until a matching \\elif , \\else , or \\endif is reached. Once an \\if or \\elif test has succeeded, the arguments of later \\elif commands in the same block are not evaluated but are treated as false. Lines following an \\else are processed only if no earlier matching \\if or \\elif succeeded. The expression argument of an \\if or \\elif command is subject to variable interpolation and backquote expansion, just like any other backslash command argument. After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer, EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "8ce3164f0726c6db12fcfde01f634f006acec0974c0cbadae292d925e62cd49a", "manual_language": "zh"}, "15": {"facts": [{"label": "\u5ba2\u6237\u7aef", "value": "psql 15.19"}, {"label": "\u533a\u5206\u5927\u5c0f\u5199\u7684\u5199\u6cd5", "value": "\\else"}], "tables": [{"key": "spellings", "rows": [{"command": {"url": "/wiki/psql/cmd-69-66/?v=15", "text": "\\if"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-69-66/?v=15", "text": "\\elif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-73-65/?v=15", "text": "\\else"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=15", "text": "\\endif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}], "title": "\u672c\u7248\u624b\u518c\u4e2d\u7684\u5199\u6cd5", "columns": [{"key": "command", "label": "\u547d\u4ee4"}, {"key": "modifiers", "label": "\u624b\u518c\u4e2d\u7684\u540e\u7f00\u4fee\u9970\u7b26"}]}], "command": "\\else", "related": [{"url": "/wiki/psql/cmd-69-66/?v=15", "label": "\\if"}, {"url": "/wiki/psql/cmd-65-6c-69-66/?v=15", "label": "\\elif"}, {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=15", "label": "\\endif"}, {"url": "/wiki/tool/psql/?v=15", "label": "psql \u547d\u4ee4\u884c\u9009\u9879\u53ca\u5b8c\u6574\u624b\u518c"}], "release": {"ref": "https://ftp.postgresql.org/pub/source/v15.19/postgresql-15.19.tar.bz2", "label": "15.19", "major": "15", "channel": "stable", "manifest": {"pdf": {"A4": {"url": "/files/documentation/pdf/15/postgresql-15-A4.pdf", "bytes": 14609140, "pages": 2987, "sha256": "66228564a4d16efb47d6a914085716ecfe22ca1566db56bc7c3d82f790646d72", "built_at": "2026-09-26"}, "US": {"url": "/files/documentation/pdf/15/postgresql-15-US.pdf", "bytes": 14495690, "pages": 3153, "sha256": "645a498c2390d47a6223ec74770631185807a19c484edb0fc5a295d9f460bc02", "built_at": "2026-09-26"}}, "tree": "15", "index": "index.html", "major": "15", "pages": 1168, "release": "15.19", "source_url": "https://ftp.postgresql.org/pub/source/v15.19/postgresql-15.19.tar.bz2", "svg_assets": 3, "source_mode": "en HTML verified against the pinned official archive", "source_sha256": "e1a64a87a46b825b88c082e4518161a47aab53c45694964f8ba1df28f7859f89"}, "revision": "6af958c6520151fc7697d56e0616b03fb00522c4568158674d452ae0644ba545", "evidence_kind": "English manual and source declarations", "source_sha256": "e1a64a87a46b825b88c082e4518161a47aab53c45694964f8ba1df28f7859f89"}, "sources": [{"url": "https://pg.center/docs/15/app-psql.html#PSQL-METACOMMAND-IF", "file": "app-psql.html", "label": "15.19 English manual \u00b7 app-psql.html", "anchor": "PSQL-METACOMMAND-IF", "sha256": "cb07228edb4914a53530afca316fd700a250cc062af2d5a74d24add93afbd0c8", "language": "en", "original_url": "/docs/15/app-psql.html#PSQL-METACOMMAND-IF"}], "sections": [], "modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "description": ["\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5 \\if \u5f00\u59cb\uff0c\u5e76\u4ee5 \\endif \u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684 \\elif \u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a \\else \u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002"], "manual_html": "
\\if expression
\\elif expression
\\else
\\endif
\n

\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5\\if\u5f00\u59cb\uff0c\u5e76\u4ee5\\endif\u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684\\elif\u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a\\else\u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002

\n

\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

\n

\u4e0e\u5176\u4ed6\u53cd\u659c\u6760\u547d\u4ee4\u53c2\u6570\u4e00\u6837\uff0c\\if \u6216 \\elif \u7684\u8868\u8fbe\u5f0f\u53c2\u6570\u5148\u8fdb\u884c\u53d8\u91cf\u63d2\u503c\u548c\u53cd\u5f15\u53f7\u5c55\u5f00\uff0c\u7136\u540e\u50cf\u5f00\u5173\u9009\u9879\u53d8\u91cf\u4e00\u6837\u6c42\u503c\u3002\u6709\u6548\u503c\u4e3a true\u3001false\u30011\u30010\u3001on\u3001off\u3001yes\u3001no \u7684\u4efb\u610f\u65e0\u6b67\u4e49\u3001\u4e0d\u533a\u5206\u5927\u5c0f\u5199\u7684\u5339\u914d\u3002\u4f8b\u5982 t\u3001T \u548c tR \u90fd\u4f1a\u89c6\u4e3a\u771f\u3002

\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

\u88ab\u8df3\u8fc7\u7684\u884c\u4f1a\u88ab\u6b63\u5e38\u89e3\u6790\u4ee5\u8bc6\u522b\u67e5\u8be2\u548c\u53cd\u659c\u7ebf\u547d\u4ee4\uff0c\u4f46\u67e5\u8be2\u4e0d\u4f1a\u53d1\u9001\u5230\u670d\u52a1\u5668\uff0c\u800c\u4e14\u9664\u4e86\u6761\u4ef6\u547d\u4ee4\uff08\\if\u3001\\elif\u3001\\else\u3001\\endif\uff09\u4e4b\u5916\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u4f1a\u88ab\u5ffd\u7565\u3002\u4ec5\u68c0\u67e5\u8df3\u8fc7\u884c\u4e2d\u6761\u4ef6\u547d\u4ee4\u7684\u6709\u6548\u5d4c\u5957\u3002\u8df3\u8fc7\u884c\u4e2d\u7684\u53d8\u91cf\u5f15\u7528\u4e0d\u4f1a\u88ab\u5c55\u5f00\uff0c\u4e5f\u4e0d\u4f1a\u6267\u884c\u53cd\u5f15\u53f7\u6269\u5c55\u3002

\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

\u4e0b\u9762\u662f\u4e00\u4e2a\u793a\u4f8b\uff1a

\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
", "manual_path": "app-psql.html#PSQL-METACOMMAND-IF", "localization": {"status": "complete", "sources": [{"url": "/docs/15/app-psql.html", "method": "same-major semantic node", "sha256": "8d6ed2e3400192f466dca73fd9423e91b9ede916fe0981b7e0cd42bc091394d2", "language": "zh", "matched_nodes": ["#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[129]/p[0]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[129]/p[3]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[129]/p[4]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[129]/p[5]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[129]/p[6]"]}], "language": "zh", "original_text": {"/versions/15/description/0": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block.", "/versions/15/facts/0/label": "Client", "/versions/15/facts/1/label": "Case-sensitive spelling", "/versions/15/tables/0/title": "Spellings in this manual definition", "/versions/15/related/3/label": "psql command-line options and complete manual", "/versions/15/tables/0/columns/0/label": "Command", "/versions/15/tables/0/columns/1/label": "Documented suffix modifiers", "/versions/15/tables/0/rows/0/modifiers": "None listed in this signature", "/versions/15/tables/0/rows/1/modifiers": "None listed in this signature", "/versions/15/tables/0/rows/2/modifiers": "None listed in this signature", "/versions/15/tables/0/rows/3/modifiers": "None listed in this signature"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "542d6477fc203bfcfae76e5feeeed7090d3ba3931f0baa0d18329037e80d0e60"}, "comparison_data": {"modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "definition": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block. The \\if and \\elif commands read their argument(s) and evaluate them as a Boolean expression. If the expression yields true then processing continues normally; otherwise, lines are skipped until a matching \\elif , \\else , or \\endif is reached. Once an \\if or \\elif test has succeeded, the arguments of later \\elif commands in the same block are not evaluated but are treated as false. Lines following an \\else are processed only if no earlier matching \\if or \\elif succeeded. The expression argument of an \\if or \\elif command is subject to variable interpolation and backquote expansion, just like any other backslash command argument. After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer, EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "8ce3164f0726c6db12fcfde01f634f006acec0974c0cbadae292d925e62cd49a", "manual_language": "zh"}, "16": {"facts": [{"label": "\u5ba2\u6237\u7aef", "value": "psql 16.15"}, {"label": "\u533a\u5206\u5927\u5c0f\u5199\u7684\u5199\u6cd5", "value": "\\else"}], "tables": [{"key": "spellings", "rows": [{"command": {"url": "/wiki/psql/cmd-69-66/?v=16", "text": "\\if"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-69-66/?v=16", "text": "\\elif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-73-65/?v=16", "text": "\\else"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=16", "text": "\\endif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}], "title": "\u672c\u7248\u624b\u518c\u4e2d\u7684\u5199\u6cd5", "columns": [{"key": "command", "label": "\u547d\u4ee4"}, {"key": "modifiers", "label": "\u624b\u518c\u4e2d\u7684\u540e\u7f00\u4fee\u9970\u7b26"}]}], "command": "\\else", "related": [{"url": "/wiki/psql/cmd-69-66/?v=16", "label": "\\if"}, {"url": "/wiki/psql/cmd-65-6c-69-66/?v=16", "label": "\\elif"}, {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=16", "label": "\\endif"}, {"url": "/wiki/tool/psql/?v=16", "label": "psql \u547d\u4ee4\u884c\u9009\u9879\u53ca\u5b8c\u6574\u624b\u518c"}], "release": {"ref": "https://ftp.postgresql.org/pub/source/v16.15/postgresql-16.15.tar.bz2", "label": "16.15", "major": "16", "channel": "stable", "manifest": {"pdf": {"A4": {"url": "/files/documentation/pdf/16/postgresql-16-A4.pdf", "bytes": 15282337, "pages": 3055, "sha256": "4bb6c1f63deedac98736d8c4c7bc0fad0ac24e85b07e21ee10411872f06afd06", "built_at": "2026-09-26"}, "US": {"url": "/files/documentation/pdf/16/postgresql-16-US.pdf", "bytes": 15164148, "pages": 3220, "sha256": "5b6b6166c89991199e144bb0ae34c17a5f29826251dbf19db1abc0df3a3e771b", "built_at": "2026-09-26"}}, "tree": "16", "index": "index.html", "major": "16", "pages": 1169, "release": "16.15", "source_url": "https://ftp.postgresql.org/pub/source/v16.15/postgresql-16.15.tar.bz2", "svg_assets": 3, "source_mode": "en HTML verified against the pinned official archive", "source_sha256": "c1575341fa7bd40f5274ea465b34390f4dc64cdd0770af327005caaeb9f6b7ed"}, "revision": "3c21e58b35318021716440e67bb8bafd392b6a2b965a244d90e9e33c99e0bdef", "evidence_kind": "English manual and source declarations", "source_sha256": "c1575341fa7bd40f5274ea465b34390f4dc64cdd0770af327005caaeb9f6b7ed"}, "sources": [{"url": "https://pg.center/docs/16/app-psql.html#PSQL-METACOMMAND-IF", "file": "app-psql.html", "label": "16.15 English manual \u00b7 app-psql.html", "anchor": "PSQL-METACOMMAND-IF", "sha256": "add25957a1dfc97db721f2958782be186ab90dc0f0a47c4b720b2b6c26172493", "language": "en", "original_url": "/docs/16/app-psql.html#PSQL-METACOMMAND-IF"}], "sections": [], "modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "description": ["\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5 \\if \u5f00\u59cb\uff0c\u5e76\u4ee5 \\endif \u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684 \\elif \u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a \\else \u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002"], "manual_html": "
\\if expression
\\elif expression
\\else
\\endif
\n

\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5\\if\u5f00\u59cb\uff0c\u5e76\u4ee5\\endif\u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684\\elif\u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a\\else\u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002

\n

\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

\n

\u4e0e\u5176\u4ed6\u53cd\u659c\u6760\u547d\u4ee4\u53c2\u6570\u4e00\u6837\uff0c\\if \u6216 \\elif \u7684\u8868\u8fbe\u5f0f\u53c2\u6570\u5148\u8fdb\u884c\u53d8\u91cf\u63d2\u503c\u548c\u53cd\u5f15\u53f7\u5c55\u5f00\uff0c\u7136\u540e\u50cf\u5f00\u5173\u9009\u9879\u53d8\u91cf\u4e00\u6837\u6c42\u503c\u3002\u6709\u6548\u503c\u4e3a true\u3001false\u30011\u30010\u3001on\u3001off\u3001yes\u3001no \u7684\u4efb\u610f\u65e0\u6b67\u4e49\u3001\u4e0d\u533a\u5206\u5927\u5c0f\u5199\u7684\u5339\u914d\u3002\u4f8b\u5982 t\u3001T \u548c tR \u90fd\u4f1a\u89c6\u4e3a\u771f\u3002

\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

\u88ab\u8df3\u8fc7\u7684\u884c\u4f1a\u88ab\u6b63\u5e38\u89e3\u6790\u4ee5\u8bc6\u522b\u67e5\u8be2\u548c\u53cd\u659c\u7ebf\u547d\u4ee4\uff0c\u4f46\u67e5\u8be2\u4e0d\u4f1a\u53d1\u9001\u5230\u670d\u52a1\u5668\uff0c\u800c\u4e14\u9664\u4e86\u6761\u4ef6\u547d\u4ee4\uff08\\if\u3001\\elif\u3001\\else\u3001\\endif\uff09\u4e4b\u5916\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u4f1a\u88ab\u5ffd\u7565\u3002\u4ec5\u68c0\u67e5\u8df3\u8fc7\u884c\u4e2d\u6761\u4ef6\u547d\u4ee4\u7684\u6709\u6548\u5d4c\u5957\u3002\u8df3\u8fc7\u884c\u4e2d\u7684\u53d8\u91cf\u5f15\u7528\u4e0d\u4f1a\u88ab\u5c55\u5f00\uff0c\u4e5f\u4e0d\u4f1a\u6267\u884c\u53cd\u5f15\u53f7\u6269\u5c55\u3002

\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

\u4e0b\u9762\u662f\u4e00\u4e2a\u793a\u4f8b\uff1a

\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
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Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block.", "/versions/16/facts/0/label": "Client", "/versions/16/facts/1/label": "Case-sensitive spelling", "/versions/16/tables/0/title": "Spellings in this manual definition", "/versions/16/related/3/label": "psql command-line options and complete manual", "/versions/16/tables/0/columns/0/label": "Command", "/versions/16/tables/0/columns/1/label": "Documented suffix modifiers", "/versions/16/tables/0/rows/0/modifiers": "None listed in this signature", "/versions/16/tables/0/rows/1/modifiers": "None listed in this signature", "/versions/16/tables/0/rows/2/modifiers": "None listed in this signature", "/versions/16/tables/0/rows/3/modifiers": "None listed in this signature"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "421e030cf3d03cc90eeef50760c064837f4678b8941fb52acc956e34e82fcae5"}, "comparison_data": {"modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "definition": "This group of commands implements nestable conditional blocks. 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\\if expression
\\elif expression
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\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

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\n

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-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
", "manual_path": "app-psql.html#PSQL-METACOMMAND-IF", "localization": {"status": "complete", "sources": [{"url": "/docs/17/app-psql.html", "method": "same-major semantic node", "sha256": "820a5ee48a79666cef06bfe375ea9337e7a347b6d32c921738edd824fe5aa9f8", "language": "zh", "matched_nodes": ["#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[133]/p[0]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[133]/p[3]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[133]/p[4]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[133]/p[5]", "#APP-PSQL/div[7]/div[3]/div[10]/dl[0]/dd[133]/p[6]"]}], "language": "zh", "original_text": {"/versions/17/description/0": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. 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A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block. The \\if and \\elif commands read their argument(s) and evaluate them as a Boolean expression. If the expression yields true then processing continues normally; otherwise, lines are skipped until a matching \\elif , \\else , or \\endif is reached. Once an \\if or \\elif test has succeeded, the arguments of later \\elif commands in the same block are not evaluated but are treated as false. Lines following an \\else are processed only if no earlier matching \\if or \\elif succeeded. The expression argument of an \\if or \\elif command is subject to variable interpolation and backquote expansion, just like any other backslash command argument. After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer, EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "8ce3164f0726c6db12fcfde01f634f006acec0974c0cbadae292d925e62cd49a", "manual_language": "zh"}, "18": {"facts": [{"label": "\u5ba2\u6237\u7aef", "value": "psql 18.6"}, {"label": "\u533a\u5206\u5927\u5c0f\u5199\u7684\u5199\u6cd5", "value": "\\else"}], "tables": [{"key": "spellings", "rows": [{"command": {"url": "/wiki/psql/cmd-69-66/?v=18", "text": "\\if"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-69-66/?v=18", "text": "\\elif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-73-65/?v=18", "text": "\\else"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=18", "text": "\\endif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}], "title": "\u672c\u7248\u624b\u518c\u4e2d\u7684\u5199\u6cd5", "columns": [{"key": "command", "label": "\u547d\u4ee4"}, {"key": "modifiers", "label": "\u624b\u518c\u4e2d\u7684\u540e\u7f00\u4fee\u9970\u7b26"}]}], "command": "\\else", "related": [{"url": "/wiki/psql/cmd-69-66/?v=18", "label": "\\if"}, {"url": "/wiki/psql/cmd-65-6c-69-66/?v=18", "label": "\\elif"}, {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=18", "label": "\\endif"}, {"url": "/wiki/tool/psql/?v=18", "label": "psql \u547d\u4ee4\u884c\u9009\u9879\u53ca\u5b8c\u6574\u624b\u518c"}], "release": {"ref": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "label": "18.6", "major": "18", "channel": "stable", "manifest": {"pdf": {"A4": {"url": "/files/documentation/pdf/18/postgresql-18-A4.pdf", "bytes": 15865106, "pages": 3154, "sha256": "19512c405da53f9f7fcf0abba359223aa65f021be025bf3411381918f92e3190", "built_at": "2026-09-26"}, "US": {"url": "/files/documentation/pdf/18/postgresql-18-US.pdf", "bytes": 15748059, "pages": 3328, "sha256": "facbe6c229e598b872d3d98bef53308f46e06746006fa4590de9a7de9dd46319", "built_at": "2026-09-26"}}, "tree": "18", "index": "index.html", "major": "18", "pages": 1148, "release": "18.6", "source_url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "svg_assets": 3, "source_mode": "en SGML built with pinned official archive", "source_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, "revision": "ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8", "evidence_kind": "English manual and source declarations", "source_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, "sources": [{"url": "https://pg.center/docs/18/app-psql.html#PSQL-METACOMMAND-IF", "file": "app-psql.html", "label": "18.6 English manual \u00b7 app-psql.html", "anchor": "PSQL-METACOMMAND-IF", "sha256": "fa2a1d39294b8854318e82e93f71272c645ed88150ecc2786c28902c3f32782c", "language": "en", "original_url": "/docs/18/app-psql.html#PSQL-METACOMMAND-IF"}], "sections": [], "modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "description": ["\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5 \\if \u5f00\u59cb\uff0c\u5e76\u4ee5 \\endif \u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684 \\elif \u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a \\else \u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002"], "manual_html": "
\\if expression
\\elif expression
\\else
\\endif
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\n

\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

\n

\u4e0e\u5176\u4ed6\u53cd\u659c\u6760\u547d\u4ee4\u53c2\u6570\u4e00\u6837\uff0c\\if \u6216 \\elif \u7684\u8868\u8fbe\u5f0f\u53c2\u6570\u5148\u8fdb\u884c\u53d8\u91cf\u63d2\u503c\u548c\u53cd\u5f15\u53f7\u5c55\u5f00\uff0c\u7136\u540e\u50cf\u5f00\u5173\u9009\u9879\u53d8\u91cf\u4e00\u6837\u6c42\u503c\u3002\u6709\u6548\u503c\u4e3a true\u3001false\u30011\u30010\u3001on\u3001off\u3001yes\u3001no \u7684\u4efb\u610f\u65e0\u6b67\u4e49\u3001\u4e0d\u533a\u5206\u5927\u5c0f\u5199\u7684\u5339\u914d\u3002\u4f8b\u5982 t\u3001T \u548c tR \u90fd\u4f1a\u89c6\u4e3a\u771f\u3002

\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

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\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

\u4e0b\u9762\u662f\u4e00\u4e2a\u793a\u4f8b\uff1a

\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
", "manual_path": "app-psql.html#PSQL-METACOMMAND-IF", "localization": {"status": "complete", "sources": [{"url": "/docs/18/app-psql.html", "method": "same-major semantic node", "sha256": "4ff5633229e0afa7feecc2750a7187d2d45a7eef0ca8febc73e4e5c15ac7fa6d", "language": "zh", "matched_nodes": ["#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[0]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[3]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[4]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[5]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[6]"]}], "language": "zh", "original_text": {"/versions/18/description/0": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block.", "/versions/18/facts/0/label": "Client", "/versions/18/facts/1/label": "Case-sensitive spelling", "/versions/18/tables/0/title": "Spellings in this manual definition", "/versions/18/related/3/label": "psql command-line options and complete manual", "/versions/18/tables/0/columns/0/label": "Command", "/versions/18/tables/0/columns/1/label": "Documented suffix modifiers", "/versions/18/tables/0/rows/0/modifiers": "None listed in this signature", "/versions/18/tables/0/rows/1/modifiers": "None listed in this signature", "/versions/18/tables/0/rows/2/modifiers": "None listed in this signature", "/versions/18/tables/0/rows/3/modifiers": "None listed in this signature"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "545ca80002f595a7e731cd3e0457ee26ac3c8c015a2cfb8a36d02b4bfe03653a"}, "comparison_data": {"modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "definition": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block. The \\if and \\elif commands read their argument(s) and evaluate them as a Boolean expression. If the expression yields true then processing continues normally; otherwise, lines are skipped until a matching \\elif , \\else , or \\endif is reached. Once an \\if or \\elif test has succeeded, the arguments of later \\elif commands in the same block are not evaluated but are treated as false. Lines following an \\else are processed only if no earlier matching \\if or \\elif succeeded. The expression argument of an \\if or \\elif command is subject to variable interpolation and backquote expansion, just like any other backslash command argument. After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer, EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "8ce3164f0726c6db12fcfde01f634f006acec0974c0cbadae292d925e62cd49a", "manual_language": "zh"}, "19": {"facts": [{"label": "\u5ba2\u6237\u7aef", "value": "psql 19beta4"}, {"label": "\u533a\u5206\u5927\u5c0f\u5199\u7684\u5199\u6cd5", "value": "\\else"}], "tables": [{"key": "spellings", "rows": [{"command": {"url": "/wiki/psql/cmd-69-66/?v=19", "text": "\\if"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-69-66/?v=19", "text": "\\elif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-73-65/?v=19", "text": "\\else"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=19", "text": "\\endif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}], "title": "\u672c\u7248\u624b\u518c\u4e2d\u7684\u5199\u6cd5", "columns": [{"key": "command", "label": "\u547d\u4ee4"}, {"key": "modifiers", "label": "\u624b\u518c\u4e2d\u7684\u540e\u7f00\u4fee\u9970\u7b26"}]}], "command": "\\else", "related": [{"url": "/wiki/psql/cmd-69-66/?v=19", "label": "\\if"}, {"url": "/wiki/psql/cmd-65-6c-69-66/?v=19", "label": "\\elif"}, {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=19", "label": "\\endif"}, {"url": "/wiki/tool/psql/?v=19", "label": "psql \u547d\u4ee4\u884c\u9009\u9879\u53ca\u5b8c\u6574\u624b\u518c"}], "release": {"ref": "https://ftp.postgresql.org/pub/source/v19beta4/postgresql-19beta4.tar.bz2", "label": "19beta4", "major": "19", "channel": "preview", "manifest": {"pdf": {"A4": {"url": "/files/documentation/pdf/19/postgresql-19-A4.pdf", "bytes": 16064841, "pages": 3052, "sha256": "4dd099e4125c591128fc5f3ebd02178dc24781f9e5ae629f96d67c4c8547427b", "built_at": "2026-09-26"}, "US": {"url": "/files/documentation/pdf/19/postgresql-19-US.pdf", "bytes": 15974616, "pages": 3225, "sha256": "61971fa857f0956d47341a0388fa6af9ae10acf691d4b2fc009007d384b0342b", "built_at": "2026-09-26"}}, "tree": "19", "index": "index.html", "major": "19", "pages": 1155, "release": "19beta4", "source_url": "https://ftp.postgresql.org/pub/source/v19beta4/postgresql-19beta4.tar.bz2", "svg_assets": 5, "source_mode": "en SGML built with pinned official archive", "source_sha256": "83157ee9c599d03b2f7a3d73ef3a56ec24e0e79cc2b3501a64d1364f56398c86"}, "revision": "1bbbbf4133d426f0e4304010688d2984c30fb67df0cc3a61b3e37eb3f6f37833", "evidence_kind": "English manual and source declarations", "source_sha256": "83157ee9c599d03b2f7a3d73ef3a56ec24e0e79cc2b3501a64d1364f56398c86"}, "sources": [{"url": "https://pg.center/docs/19/app-psql.html#PSQL-METACOMMAND-IF", "file": "app-psql.html", "label": "19beta4 English manual \u00b7 app-psql.html", "anchor": "PSQL-METACOMMAND-IF", "sha256": "312975c12d6e4d62aeebcb5e98e7ca795c6d07ecb743b4bc64403dc42bc2a6e9", "language": "en", "original_url": "/docs/19/app-psql.html#PSQL-METACOMMAND-IF"}], "sections": [], "modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "description": ["\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5 \\if \u5f00\u59cb\uff0c\u5e76\u4ee5 \\endif \u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684 \\elif \u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a \\else \u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002"], "manual_html": "
\\if expression
\\elif expression
\\else
\\endif
\n

\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5\\if\u5f00\u59cb\uff0c\u5e76\u4ee5\\endif\u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684\\elif\u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a\\else\u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002

\n

\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

\n

\u4e0e\u5176\u4ed6\u53cd\u659c\u6760\u547d\u4ee4\u53c2\u6570\u4e00\u6837\uff0c\\if \u6216 \\elif \u7684\u8868\u8fbe\u5f0f\u53c2\u6570\u5148\u8fdb\u884c\u53d8\u91cf\u63d2\u503c\u548c\u53cd\u5f15\u53f7\u5c55\u5f00\uff0c\u7136\u540e\u50cf\u5f00\u5173\u9009\u9879\u53d8\u91cf\u4e00\u6837\u6c42\u503c\u3002\u6709\u6548\u503c\u4e3a true\u3001false\u30011\u30010\u3001on\u3001off\u3001yes\u3001no \u7684\u4efb\u610f\u65e0\u6b67\u4e49\u3001\u4e0d\u533a\u5206\u5927\u5c0f\u5199\u7684\u5339\u914d\u3002\u4f8b\u5982 t\u3001T \u548c tR \u90fd\u4f1a\u89c6\u4e3a\u771f\u3002

\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

\u88ab\u8df3\u8fc7\u7684\u884c\u4f1a\u88ab\u6b63\u5e38\u89e3\u6790\u4ee5\u8bc6\u522b\u67e5\u8be2\u548c\u53cd\u659c\u7ebf\u547d\u4ee4\uff0c\u4f46\u67e5\u8be2\u4e0d\u4f1a\u53d1\u9001\u5230\u670d\u52a1\u5668\uff0c\u800c\u4e14\u9664\u4e86\u6761\u4ef6\u547d\u4ee4\uff08\\if\u3001\\elif\u3001\\else\u3001\\endif\uff09\u4e4b\u5916\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u4f1a\u88ab\u5ffd\u7565\u3002\u4ec5\u68c0\u67e5\u8df3\u8fc7\u884c\u4e2d\u6761\u4ef6\u547d\u4ee4\u7684\u6709\u6548\u5d4c\u5957\u3002\u8df3\u8fc7\u884c\u4e2d\u7684\u53d8\u91cf\u5f15\u7528\u4e0d\u4f1a\u88ab\u5c55\u5f00\uff0c\u4e5f\u4e0d\u4f1a\u6267\u884c\u53cd\u5f15\u53f7\u6269\u5c55\u3002

\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

\u4e0b\u9762\u662f\u4e00\u4e2a\u793a\u4f8b\uff1a

\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS (SELECT 1 FROM customer WHERE customer_id = 123) AS is_customer,\n    EXISTS (SELECT 1 FROM employee WHERE employee_id = 456) AS is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
", "manual_path": "app-psql.html#PSQL-METACOMMAND-IF", "localization": {"status": "complete", "sources": [{"url": "/docs/19/app-psql.html", "method": "same-major semantic node", "sha256": "1351be06967585f99a84454a26dff346091ea378daf6c7ed9fa18edee9d1131c", "language": "zh", "matched_nodes": ["#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[0]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[3]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[4]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[5]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[6]"]}], "language": "zh", "original_text": {"/versions/19/description/0": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block.", "/versions/19/facts/0/label": "Client", "/versions/19/facts/1/label": "Case-sensitive spelling", "/versions/19/tables/0/title": "Spellings in this manual definition", "/versions/19/related/3/label": "psql command-line options and complete manual", "/versions/19/tables/0/columns/0/label": "Command", "/versions/19/tables/0/columns/1/label": "Documented suffix modifiers", "/versions/19/tables/0/rows/0/modifiers": "None listed in this signature", "/versions/19/tables/0/rows/1/modifiers": "None listed in this signature", "/versions/19/tables/0/rows/2/modifiers": "None listed in this signature", "/versions/19/tables/0/rows/3/modifiers": "None listed in this signature"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "0d96bde1ffebbbd2bc1a442f9667d42a90881fadef30e3709b916159a419b8d2"}, "comparison_data": {"modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "definition": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block. The \\if and \\elif commands read their argument(s) and evaluate them as a Boolean expression. If the expression yields true then processing continues normally; otherwise, lines are skipped until a matching \\elif , \\else , or \\endif is reached. Once an \\if or \\elif test has succeeded, the arguments of later \\elif commands in the same block are not evaluated but are treated as false. Lines following an \\else are processed only if no earlier matching \\if or \\elif succeeded. The expression argument of an \\if or \\elif command is subject to variable interpolation and backquote expansion, just like any other backslash command argument. After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS (SELECT 1 FROM customer WHERE customer_id = 123) AS is_customer, EXISTS (SELECT 1 FROM employee WHERE employee_id = 456) AS is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "2fa0e95773c574cd8d1dcb28da1c7b9e69ffe9397735cafd621ba82f01e7cc31", "manual_language": "zh"}, "20": {"facts": [{"label": "\u5ba2\u6237\u7aef", "value": "psql 20devel"}, {"label": "\u533a\u5206\u5927\u5c0f\u5199\u7684\u5199\u6cd5", "value": "\\else"}], "tables": [{"key": "spellings", "rows": [{"command": {"url": "/wiki/psql/cmd-69-66/?v=20", "text": "\\if"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-69-66/?v=20", "text": "\\elif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6c-73-65/?v=20", "text": "\\else"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}, {"command": {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=20", "text": "\\endif"}, "modifiers": "\u6b64\u8bed\u6cd5\u7b7e\u540d\u672a\u5217\u51fa"}], "title": "\u672c\u7248\u624b\u518c\u4e2d\u7684\u5199\u6cd5", "columns": [{"key": "command", "label": "\u547d\u4ee4"}, {"key": "modifiers", "label": "\u624b\u518c\u4e2d\u7684\u540e\u7f00\u4fee\u9970\u7b26"}]}], "command": "\\else", "related": [{"url": "/wiki/psql/cmd-69-66/?v=20", "label": "\\if"}, {"url": "/wiki/psql/cmd-65-6c-69-66/?v=20", "label": "\\elif"}, {"url": "/wiki/psql/cmd-65-6e-64-69-66/?v=20", "label": "\\endif"}, {"url": "/wiki/tool/psql/?v=20", "label": "psql \u547d\u4ee4\u884c\u9009\u9879\u53ca\u5b8c\u6574\u624b\u518c"}], "release": {"ref": "https://ftp.postgresql.org/pub/snapshot/dev/postgresql-snapshot.tar.bz2", "label": "20devel", "major": "20", "channel": "devel", "manifest": {"pdf": {"A4": {"url": "/files/documentation/pdf/20/postgresql-20-A4.pdf", "bytes": 16030631, "pages": 3052, "sha256": "bd5d82c0ce38fc18f92a0447818a91a193a261776bca1c37564bf9a683e177d0", "built_at": "2026-09-28"}, "US": {"url": "/files/documentation/pdf/20/postgresql-20-US.pdf", "bytes": 15936613, "pages": 3223, "sha256": "d97d9e0db479a02f4234b175f50fcad70c3661619afc8d6df9b9437882e3c299", "built_at": "2026-09-28"}}, "tree": "0", "index": "index.html", "major": "20", "pages": 1156, "release": "20devel", "source_url": "https://ftp.postgresql.org/pub/snapshot/dev/postgresql-snapshot.tar.bz2", "svg_assets": 6, "source_mode": "en SGML built with pinned official archive", "source_sha256": "4d3346909b201ac1648232cf290462a7070c119326f56196f1f0253ed80fae41", "source_snapshot_utc": "26-Sep-2026 20:22"}, "revision": "2eba5e0fd4c3bffb2803247b6cd537878e9d6ee5a6dfbe3c50ece8b421b80918", "evidence_kind": "English manual and source declarations", "source_sha256": "4d3346909b201ac1648232cf290462a7070c119326f56196f1f0253ed80fae41"}, "sources": [{"url": "https://pg.center/docs/devel/app-psql.html#PSQL-METACOMMAND-IF", "file": "app-psql.html", "label": "20devel English manual \u00b7 app-psql.html", "anchor": "PSQL-METACOMMAND-IF", "sha256": "6df5f6fbaff7800ae0e4a08a3116090d890a0cdcc02fddc31c1f220725905f87", "language": "en", "original_url": "/docs/devel/app-psql.html#PSQL-METACOMMAND-IF"}], "sections": [], "modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "description": ["\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5 \\if \u5f00\u59cb\uff0c\u5e76\u4ee5 \\endif \u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684 \\elif \u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a \\else \u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002"], "manual_html": "
\\if expression
\\elif expression
\\else
\\endif
\n

\u8fd9\u7ec4\u547d\u4ee4\u5b9e\u73b0\u4e86\u53ef\u5d4c\u5957\u7684\u6761\u4ef6\u5757\u3002\u6761\u4ef6\u5757\u5fc5\u987b\u4ee5\\if\u5f00\u59cb\uff0c\u5e76\u4ee5\\endif\u7ed3\u675f\u3002\u5728\u4e24\u8005\u4e4b\u95f4\u53ef\u4ee5\u6709\u4efb\u610f\u6570\u91cf\u7684\\elif\u5b50\u53e5\uff0c\u540e\u9762\u53ef\u4ee5\u9009\u62e9\u6027\u5730\u8ddf\u7740\u4e00\u4e2a\\else\u5b50\u53e5\u3002\u5728\u5f62\u6210\u6761\u4ef6\u5757\u7684\u547d\u4ee4\u4e4b\u95f4\u901a\u5e38\u4f1a\u51fa\u73b0\u666e\u901a\u67e5\u8be2\u548c\u5176\u4ed6\u7c7b\u578b\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u3002

\n

\\if \u548c \\elif \u8bfb\u53d6\u53c2\u6570\u5e76\u5c06\u5176\u4f5c\u4e3a\u5e03\u5c14\u8868\u8fbe\u5f0f\u6c42\u503c\u3002\u7ed3\u679c\u4e3a\u771f\u65f6\u7ee7\u7eed\u6b63\u5e38\u5904\u7406\uff0c\u5426\u5219\u8df3\u8fc7\u540e\u7eed\u884c\uff0c\u76f4\u5230\u9047\u5230\u5339\u914d\u7684 \\elif\u3001\\else \u6216 \\endif\u3002\u67d0\u4e2a \\if \u6216 \\elif \u6761\u4ef6\u6210\u7acb\u540e\uff0c\u540c\u4e00\u5757\u4e2d\u540e\u7eed \\elif \u7684\u53c2\u6570\u4e0d\u518d\u6c42\u503c\uff0c\u76f4\u63a5\u89c6\u4e3a\u5047\u3002\u53ea\u6709\u4e4b\u524d\u5339\u914d\u7684 \\if \u548c \\elif \u5747\u672a\u6210\u7acb\uff0c\u624d\u5904\u7406 \\else \u540e\u7684\u884c\u3002

\n

\u4e0e\u5176\u4ed6\u53cd\u659c\u6760\u547d\u4ee4\u53c2\u6570\u4e00\u6837\uff0c\\if \u6216 \\elif \u7684\u8868\u8fbe\u5f0f\u53c2\u6570\u5148\u8fdb\u884c\u53d8\u91cf\u63d2\u503c\u548c\u53cd\u5f15\u53f7\u5c55\u5f00\uff0c\u7136\u540e\u50cf\u5f00\u5173\u9009\u9879\u53d8\u91cf\u4e00\u6837\u6c42\u503c\u3002\u6709\u6548\u503c\u4e3a true\u3001false\u30011\u30010\u3001on\u3001off\u3001yes\u3001no \u7684\u4efb\u610f\u65e0\u6b67\u4e49\u3001\u4e0d\u533a\u5206\u5927\u5c0f\u5199\u7684\u5339\u914d\u3002\u4f8b\u5982 t\u3001T \u548c tR \u90fd\u4f1a\u89c6\u4e3a\u771f\u3002

\n

\u4e0d\u80fd\u6b63\u786e\u6c42\u503c\u4e3a\u771f\u6216\u5047\u7684\u8868\u8fbe\u5f0f\u4f1a\u4ea7\u751f\u8b66\u544a\uff0c\u5e76\u88ab\u89c6\u4e3a\u5047\u3002

\n

\u88ab\u8df3\u8fc7\u7684\u884c\u4f1a\u88ab\u6b63\u5e38\u89e3\u6790\u4ee5\u8bc6\u522b\u67e5\u8be2\u548c\u53cd\u659c\u7ebf\u547d\u4ee4\uff0c\u4f46\u67e5\u8be2\u4e0d\u4f1a\u53d1\u9001\u5230\u670d\u52a1\u5668\uff0c\u800c\u4e14\u9664\u4e86\u6761\u4ef6\u547d\u4ee4\uff08\\if\u3001\\elif\u3001\\else\u3001\\endif\uff09\u4e4b\u5916\u7684\u53cd\u659c\u7ebf\u547d\u4ee4\u4f1a\u88ab\u5ffd\u7565\u3002\u4ec5\u68c0\u67e5\u8df3\u8fc7\u884c\u4e2d\u6761\u4ef6\u547d\u4ee4\u7684\u6709\u6548\u5d4c\u5957\u3002\u8df3\u8fc7\u884c\u4e2d\u7684\u53d8\u91cf\u5f15\u7528\u4e0d\u4f1a\u88ab\u5c55\u5f00\uff0c\u4e5f\u4e0d\u4f1a\u6267\u884c\u53cd\u5f15\u53f7\u6269\u5c55\u3002

\n

\u540c\u4e00\u4e2a\u6761\u4ef6\u5757\u7684\u6240\u6709\u53cd\u659c\u7ebf\u547d\u4ee4\u5fc5\u987b\u51fa\u73b0\u5728\u540c\u4e00\u4e2a\u6e90\u6587\u4ef6\u4e2d\u3002\u5982\u679c\u4e3b\u8f93\u5165\u6587\u4ef6\u6216\u901a\u8fc7\\include\u5f15\u5165\u7684\u6587\u4ef6\u5230\u8fbe EOF \u65f6\uff0c\u4ecd\u6709\u672c\u5730\\if\u5757\u672a\u5173\u95ed\uff0cpsql\u5c31\u4f1a\u62a5\u9519\u3002

\n

\u4e0b\u9762\u662f\u4e00\u4e2a\u793a\u4f8b\uff1a

\n
-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS (SELECT 1 FROM customer WHERE customer_id = 123) AS is_customer,\n    EXISTS (SELECT 1 FROM employee WHERE employee_id = 456) AS is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
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-- check for the existence of two separate records in the database and store\n-- the results in separate psql variables\nSELECT\n    EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer,\n    EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee\n\\gset\n\\if :is_customer\n    SELECT * FROM customer WHERE customer_id = 123;\n\\elif :is_employee\n    \\echo 'is not a customer but is an employee'\n    SELECT * FROM employee WHERE employee_id = 456;\n\\else\n    \\if yes\n        \\echo 'not a customer or employee'\n    \\else\n        \\echo 'this will never print'\n    \\endif\n\\endif\n
\n
", "manual_path": "app-psql.html#PSQL-METACOMMAND-IF", "localization": {"status": "complete", "sources": [{"url": "/docs/18/app-psql.html", "method": "same-major semantic node", "sha256": "4ff5633229e0afa7feecc2750a7187d2d45a7eef0ca8febc73e4e5c15ac7fa6d", "language": "zh", "matched_nodes": ["#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[0]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[3]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[4]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[5]", "#APP-PSQL/div[7]/div[3]/div[11]/dl[0]/dd[137]/p[6]"]}], "language": "zh", "original_text": {"/versions/18/description/0": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block.", "/versions/18/facts/0/label": "Client", "/versions/18/facts/1/label": "Case-sensitive spelling", "/versions/18/tables/0/title": "Spellings in this manual definition", "/versions/18/related/3/label": "psql command-line options and complete manual", "/versions/18/tables/0/columns/0/label": "Command", "/versions/18/tables/0/columns/1/label": "Documented suffix modifiers", "/versions/18/tables/0/rows/0/modifiers": "None listed in this signature", "/versions/18/tables/0/rows/1/modifiers": "None listed in this signature", "/versions/18/tables/0/rows/2/modifiers": "None listed in this signature", "/versions/18/tables/0/rows/3/modifiers": "None listed in this signature"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "545ca80002f595a7e731cd3e0457ee26ac3c8c015a2cfb8a36d02b4bfe03653a"}, "comparison_data": {"modifiers": [], "signature": "\\if expression \\elif expression \\else \\endif", "spellings": ["\\if", "\\elif", "\\else", "\\endif"], "definition": "This group of commands implements nestable conditional blocks. A conditional block must begin with an \\if and end with an \\endif . In between there may be any number of \\elif clauses, which may optionally be followed by a single \\else clause. Ordinary queries and other types of backslash commands may (and usually do) appear between the commands forming a conditional block. The \\if and \\elif commands read their argument(s) and evaluate them as a Boolean expression. If the expression yields true then processing continues normally; otherwise, lines are skipped until a matching \\elif , \\else , or \\endif is reached. Once an \\if or \\elif test has succeeded, the arguments of later \\elif commands in the same block are not evaluated but are treated as false. Lines following an \\else are processed only if no earlier matching \\if or \\elif succeeded. The expression argument of an \\if or \\elif command is subject to variable interpolation and backquote expansion, just like any other backslash command argument. After that it is evaluated like the value of an on/off option variable. So a valid value is any unambiguous case-insensitive match for one of: true , false , 1 , 0 , on , off , yes , no . For example, t , T , and tR will all be considered to be true . Expressions that do not properly evaluate to true or false will generate a warning and be treated as false. Lines being skipped are parsed normally to identify queries and backslash commands, but queries are not sent to the server, and backslash commands other than conditionals ( \\if , \\elif , \\else , \\endif ) are ignored. Conditional commands are checked only for valid nesting. Variable references in skipped lines are not expanded, and backquote expansion is not performed either. All the backslash commands of a given conditional block must appear in the same source file. If EOF is reached on the main input file or an \\include -ed file before all local \\if -blocks have been closed, then psql will raise an error. Here is an example: -- check for the existence of two separate records in the database and store -- the results in separate psql variables SELECT EXISTS(SELECT 1 FROM customer WHERE customer_id = 123) as is_customer, EXISTS(SELECT 1 FROM employee WHERE employee_id = 456) as is_employee \\gset \\if :is_customer SELECT * FROM customer WHERE customer_id = 123; \\elif :is_employee \\echo 'is not a customer but is an employee' SELECT * FROM employee WHERE employee_id = 456; \\else \\if yes \\echo 'not a customer or employee' \\else \\echo 'this will never print' \\endif \\endif"}, "comparison_hash": "8ce3164f0726c6db12fcfde01f634f006acec0974c0cbadae292d925e62cd49a", "manual_language": "zh"}, "comparison": {"left": "17", "right": "18", "status": "unchanged", "diff": ""}}