{"id":5183,"date":"2024-11-14T08:58:44","date_gmt":"2024-11-14T00:58:44","guid":{"rendered":"https:\/\/fwq.ai\/blog\/5183\/"},"modified":"2024-11-14T08:58:44","modified_gmt":"2024-11-14T00:58:44","slug":"sql%e4%b8%ad%e7%9a%84case-when%e7%94%a8%e6%b3%95","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/5183\/","title":{"rendered":"sql\u4e2d\u7684case when\u7528\u6cd5"},"content":{"rendered":"

\n sql \u4e2d case when \u8bed\u53e5\u63d0\u4f9b\u4e86\u4e00\u79cd\u6839\u636e\u6761\u4ef6\u6267\u884c\u4e0d\u540c\u67e5\u8be2\u7684\u65b9\u6cd5\u3002\u5b83\u91c7\u7528\u4ee5\u4e0b\u8bed\u6cd5\uff1acase when condition1 then result1 when condition2 then result2 … else default_result end\u3002\u8be5\u8bed\u53e5\u8bc4\u4f30\u6761\u4ef6\uff0c\u6267\u884c\u5339\u914d\u9879\u5173\u8054\u7684\u7ed3\u679c\uff0c\u5982\u679c\u6ca1\u6709\u5339\u914d\u9879\uff0c\u5219\u8fd4\u56de\u9ed8\u8ba4\u7ed3\u679c\u3002case when \u8bed\u53e5\u7684\u4f18\u70b9\u5305\u62ec\u7b80\u5316\u590d\u6742\u7684\u67e5\u8be2\u3001\u63d0\u9ad8\u6027\u80fd\u548c\u589e\u5f3a\u7075\u6d3b\u6027\u3002\u5728\u4f7f\u7528\u8be5\u8bed\u53e5\u65f6\uff0c\u8bf7\u786e\u4fdd\u6761\u4ef6\u4e92\u65a5\u5e76\u63d0\u4f9b else \u5b50\u53e5\u4ee5\u5904\u7406\u6240\u6709\u60c5\u51b5\u3002\n<\/p><\/blockquote>\n

\"sql\u4e2d\u7684case<\/p>\n

SQL \u4e2d\u7684 CASE WHEN \u7528\u6cd5<\/strong><\/p>\n

\u5728 SQL \u4e2d\uff0cCASE WHEN \u8bed\u53e5\u7528\u4e8e\u6839\u636e\u6307\u5b9a\u7684\u6761\u4ef6\u6267\u884c\u4e0d\u540c\u7684\u67e5\u8be2\u3002\u5b83\u662f\u4e00\u79cd\u5f3a\u5927\u4e14\u7075\u6d3b\u7684\u5de5\u5177\uff0c\u53ef\u4ee5\u7528\u4e8e\u5404\u79cd\u7c7b\u578b\u7684\u67e5\u8be2\uff0c\u5305\u62ec\u590d\u6742\u7684\u4e1a\u52a1\u903b\u8f91\u548c\u6570\u636e\u8f6c\u6362\u3002<\/p>\n

\u8bed\u6cd5<\/strong><\/p>\n

CASE\n    WHEN condition1 THEN result1\n    WHEN condition2 THEN result2\n    ...\n    ELSE default_result\nEND<\/pre>\n
  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
\u793a\u4f8b<\/strong><\/p>\n
\u4ee5\u4e0b\u793a\u4f8b\u5c55\u793a\u4e86\u5982\u4f55\u4f7f\u7528 CASE WHEN \u8bed\u53e5\u6839\u636e\u5b66\u751f\u6210\u7ee9\u786e\u5b9a\u5176\u7b49\u7ea7\uff1a<\/p>\n
SELECT\n    student_name,\n    score,\n    CASE\n        WHEN score >= 90 THEN 'A'\n        WHEN score >= 80 THEN 'B'\n        WHEN score >= 70 THEN 'C'\n        ELSE 'F'\n    END AS letter_grade\nFROM students;<\/pre>\n
  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
\u5de5\u4f5c\u539f\u7406<\/strong><\/p>\n
CASE WHEN \u8bed\u53e5\u7684\u5de5\u4f5c\u539f\u7406\u5982\u4e0b\uff1a<\/p>\n
    \n
  1.  \u8bc4\u4f30\u6761\u4ef6\uff1a<\/strong>\u8bed\u53e5\u4ece\u9876\u90e8\u5f00\u59cb\u8bc4\u4f30\u6761\u4ef6\u3002<\/li>\n
  2.  \u6267\u884c\u5339\u914d\u7ed3\u679c\uff1a<\/strong>\u5982\u679c\u67d0\u4e2a\u6761\u4ef6\u4e3a true\uff0c\u5219\u6267\u884c\u4e0e\u8be5\u6761\u4ef6\u5173\u8054\u7684\u7ed3\u679c\u3002<\/li>\n
  3.  \u91cd\u590d\u6b65\u9aa4\uff1a<\/strong>\u8bed\u53e5\u7ee7\u7eed\u8bc4\u4f30\u6761\u4ef6\uff0c\u76f4\u5230\u627e\u5230\u5339\u914d\u9879\u6216\u5230\u8fbe ELSE \u5b50\u53e5\u3002<\/li>\n
  4.  \u8fd4\u56de\u7ed3\u679c\uff1a<\/strong>\u5982\u679c\u627e\u5230\u5339\u914d\u9879\uff0c\u5219\u8fd4\u56de\u5173\u8054\u7684\u7ed3\u679c\uff1b\u5982\u679c\u627e\u4e0d\u5230\u5339\u914d\u9879\uff0c\u5219\u8fd4\u56de ELSE \u5b50\u53e5\u4e2d\u7684\u9ed8\u8ba4\u7ed3\u679c\u3002<\/li>\n<\/ol>\n
    \u4f18\u70b9<\/strong><\/p>\n
    \u4f7f\u7528 CASE WHEN \u8bed\u53e5\u6709\u51e0\u4e2a\u4f18\u70b9\uff1a<\/p>\n
      \n
    •  \u7b80\u5316\u590d\u6742\u7684\u67e5\u8be2\uff1a<\/strong>\u5b83\u53ef\u4ee5\u5c06\u591a\u4e2a IF-ELSE \u8bed\u53e5\u7ec4\u5408\u5230\u4e00\u4e2a\u7b80\u6d01\u7684\u8bed\u53e5\u4e2d\u3002<\/li>\n
    •  \u63d0\u9ad8\u6027\u80fd\uff1a<\/strong>\u5b83\u53ef\u4ee5\u4f18\u5316\u67e5\u8be2\uff0c\u56e0\u4e3a SQL \u5f15\u64ce\u53ef\u4ee5\u4e00\u6b21\u6027\u8bc4\u4f30\u6240\u6709\u6761\u4ef6\u3002<\/li>\n
    •  \u589e\u5f3a\u7075\u6d3b\u6027\uff1a<\/strong>\u5b83\u5141\u8bb8\u6839\u636e\u52a8\u6001\u6216\u590d\u6742\u7684\u89c4\u5219\u8f7b\u677e\u5730\u8f6c\u6362\u6570\u636e\u3002<\/li>\n<\/ul>\n
      \u6ce8\u610f\u4e8b\u9879<\/strong><\/p>\n
      \u4f7f\u7528 CASE WHEN \u8bed\u53e5\u65f6\uff0c\u9700\u8981\u6ce8\u610f\u4ee5\u4e0b\u4e8b\u9879\uff1a<\/p>\n
        \n
      • \u786e\u4fdd\u6761\u4ef6\u662f\u4e92\u65a5\u7684\uff0c\u4ee5\u9632\u6b62\u91cd\u53e0\u3002<\/li>\n
      • \u63d0\u4f9b ELSE \u5b50\u53e5\u4ee5\u5904\u7406\u6240\u6709\u53ef\u80fd\u7684\u60c5\u51b5\u3002<\/li>\n
      • \u8003\u8651\u4f7f\u7528 CASE \u8868\u8fbe\u5f0f\u66ff\u6362\u590d\u6742\u7684 CASE WHEN \u8bed\u53e5\uff0c\u4ee5\u63d0\u9ad8\u53ef\u8bfb\u6027\u548c\u53ef\u7ef4\u62a4\u6027\u3002<\/li>\n<\/ul>\n
        \u4ee5\u4e0a\u5c31\u662fsql\u4e2d\u7684case when\u7528\u6cd5\u7684\u8be6\u7ec6\u5185\u5bb9\uff0c\u66f4\u591a\u8bf7\u5173\u6ce8\u7c73\u4e91\u7f51\u5176\u5b83\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
        sql \u4e2d case when \u8bed\u53e5\u63d0\u4f9b\u4e86\u4e00\u79cd\u6839\u636e\u6761\u4ef6\u6267\u884c\u4e0d\u540c\u67e5\u8be2\u7684\u65b9\u6cd5\u3002\u5b83\u91c7\u7528\u4ee5\u4e0b\u8bed\u6cd5\uff1acase when condition1 then result1 when condition2 then result2 … else default_result end\u3002\u8be5\u8bed\u53e5\u8bc4\u4f30\u6761\u4ef6\uff0c\u6267\u884c\u5339\u914d\u9879\u5173\u8054\u7684\u7ed3\u679c\uff0c\u5982\u679c\u6ca1\u6709\u5339\u914d\u9879\uff0c\u5219\u8fd4\u56de\u9ed8\u8ba4\u7ed3\u679c\u3002case when \u8bed\u53e5\u7684\u4f18\u70b9\u5305\u62ec\u7b80\u5316\u590d\u6742\u7684\u67e5\u8be2\u3001\u63d0\u9ad8\u6027\u80fd\u548c\u589e\u5f3a\u7075\u6d3b\u6027\u3002\u5728\u4f7f\u7528\u8be5\u8bed\u53e5\u65f6\uff0c\u8bf7\u786e\u4fdd\u6761\u4ef6\u4e92\u65a5\u5e76\u63d0\u4f9b else \u5b50\u53e5\u4ee5\u5904\u7406\u6240\u6709\u60c5\u51b5\u3002 SQL \u4e2d\u7684 CASE WHEN \u7528\u6cd5 \u5728 SQL \u4e2d\uff0cCASE WHEN \u8bed\u53e5\u7528\u4e8e\u6839\u636e\u6307\u5b9a\u7684\u6761\u4ef6\u6267\u884c\u4e0d\u540c\u7684\u67e5\u8be2\u3002\u5b83\u662f\u4e00\u79cd\u5f3a\u5927\u4e14\u7075\u6d3b\u7684\u5de5\u5177\uff0c\u53ef\u4ee5\u7528\u4e8e\u5404\u79cd\u7c7b\u578b\u7684\u67e5\u8be2\uff0c\u5305\u62ec\u590d\u6742\u7684\u4e1a\u52a1\u903b\u8f91\u548c\u6570\u636e\u8f6c\u6362\u3002 \u8bed\u6cd5 CASE WHEN condition1 THEN result1 WHEN condition2 THEN result2 … ELSE default_result END \u767b\u5f55\u540e\u590d\u5236 \u793a\u4f8b \u4ee5\u4e0b\u793a\u4f8b\u5c55\u793a\u4e86\u5982\u4f55\u4f7f\u7528 CASE WHEN \u8bed\u53e5\u6839\u636e\u5b66\u751f\u6210\u7ee9\u786e\u5b9a\u5176\u7b49\u7ea7\uff1a SELECT student_name, score, CASE […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-5183","post","type-post","status-publish","format-standard","hentry","category-16"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/5183","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/comments?post=5183"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/5183\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=5183"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=5183"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=5183"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}