{"id":5202,"date":"2024-11-14T08:26:14","date_gmt":"2024-11-14T00:26:14","guid":{"rendered":"https:\/\/fwq.ai\/blog\/5202\/"},"modified":"2024-11-14T08:26:14","modified_gmt":"2024-11-14T00:26:14","slug":"sql%e4%b8%adcase-when%e5%a4%9a%e7%a7%8d%e7%94%a8%e6%b3%95","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/5202\/","title":{"rendered":"sql\u4e2dcase when\u591a\u79cd\u7528\u6cd5"},"content":{"rendered":"

\n case when \u8bed\u53e5\u53ef\u7528\u4e8e\u6839\u636e\u6761\u4ef6\u8fd4\u56de\u4e0d\u540c\u503c\uff0c\u5904\u7406\u591a\u91cd\u6761\u4ef6\u3001\u641c\u7d22\u7279\u5b9a\u503c\u3001\u8f6c\u6362\u6570\u636e\u7c7b\u578b\u3001\u5e94\u7528\u5230\u591a\u4e2a\u5217\uff0c\u4ee5\u53ca\u53d6\u4ee3 null \u503c\u3002\n<\/p><\/blockquote>\n

\"sql\u4e2dcase<\/p>\n

SQL \u4e2d CASE WHEN \u7684\u591a\u79cd\u7528\u6cd5<\/strong><\/p>\n

CASE WHEN \u8bed\u53e5\u5728 SQL \u4e2d\u7528\u4e8e\u6839\u636e\u6307\u5b9a\u7684\u6761\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u503c\u3002\u5b83\u662f\u4e00\u79cd\u5f3a\u5927\u7684\u5de5\u5177\uff0c\u53ef\u4ee5\u6267\u884c\u5404\u79cd\u6570\u636e\u8f6c\u6362\u548c\u67e5\u8be2\u64cd\u4f5c\u3002<\/p>\n

\u57fa\u672c\u7528\u6cd5<\/strong><\/p>\n

\u6700\u57fa\u672c\u7684\u5f62\u5f0f\u5982\u4e0b\uff1a<\/p>\n

CASE WHEN <condition> THEN <value_if_true> ELSE <value_if_false> END<\/pre>\n
  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
    \n
  •    \uff1a <\/strong>\u8981\u8bc4\u4f30\u7684\u6761\u4ef6\u3002<\/li>\n
  •    \uff1a <\/strong>\u5982\u679c\u6761\u4ef6\u4e3a true \u65f6\u8981\u8fd4\u56de\u7684\u503c\u3002<\/li>\n
  •    \uff1a <\/strong>\u5982\u679c\u6761\u4ef6\u4e3a false \u65f6\u8981\u8fd4\u56de\u7684\u503c\u3002<\/li>\n<\/ul>\n
    \u591a\u91cd\u6761\u4ef6<\/strong><\/p>\n
    CASE WHEN \u8bed\u53e5\u53ef\u4ee5\u5904\u7406\u591a\u4e2a\u6761\u4ef6\uff0c\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
    CASE\n    WHEN <condition1> THEN <value_if_true1>\n    WHEN <condition2> THEN <value_if_true2>\n    ...\n    ELSE <value_if_no_match>\nEND<\/pre>\n
      \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
    \u641c\u7d22\u7279\u5b9a\u503c<\/strong><\/p>\n
    CASE WHEN \u8bed\u53e5\u53ef\u7528\u4e8e\u641c\u7d22\u7279\u5b9a\u503c\uff0c\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
    CASE <expression>\n    WHEN <value1> THEN <value_if_found1>\n    WHEN <value2> THEN <value_if_found2>\n    ...\n    ELSE <value_if_not_found>\nEND<\/pre>\n
      \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
    \u8f6c\u6362\u6570\u636e\u7c7b\u578b<\/strong><\/p>\n
    CASE WHEN \u8bed\u53e5\u53ef\u7528\u4e8e\u5c06\u6570\u636e\u4ece\u4e00\u79cd\u7c7b\u578b\u8f6c\u6362\u4e3a\u53e6\u4e00\u79cd\u7c7b\u578b\uff0c\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
    CASE <expression>\n    WHEN <value1> THEN CAST(<expression> AS <new_type>)\n    ...\n    ELSE CAST(<expression> AS <new_type>)\nEND<\/pre>\n
      \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
    \u5e94\u7528\u5230\u591a\u4e2a\u5217<\/strong><\/p>\n
    CASE WHEN \u8bed\u53e5\u53ef\u4ee5\u5e94\u7528\u5230\u591a\u4e2a\u5217\uff0c\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
    SELECT\n    CASE <condition> THEN <value_for_column1> ELSE <value_for_column2> END AS <new_column_name>,\n    ...\n    CASE <condition> THEN <value_for_columnn> ELSE <value_for_columnn> END AS <new_column_name>\nFROM <table_name>;<\/pre>\n
      \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
    \u53d6\u4ee3 NULL \u503c<\/strong><\/p>\n
    CASE WHEN \u8bed\u53e5\u53ef\u7528\u4e8e\u53d6\u4ee3 NULL \u503c\uff0c\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
    CASE\n    WHEN <expression> IS NULL THEN <value_to_replace>\n    ELSE <expression>\nEND<\/pre>\n
      \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
    \u4ee5\u4e0a\u5c31\u662fsql\u4e2dcase when\u591a\u79cd\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":"
    case when \u8bed\u53e5\u53ef\u7528\u4e8e\u6839\u636e\u6761\u4ef6\u8fd4\u56de\u4e0d\u540c\u503c\uff0c\u5904\u7406\u591a\u91cd\u6761\u4ef6\u3001\u641c\u7d22\u7279\u5b9a\u503c\u3001\u8f6c\u6362\u6570\u636e\u7c7b\u578b\u3001\u5e94\u7528\u5230\u591a\u4e2a\u5217\uff0c\u4ee5\u53ca\u53d6\u4ee3 null \u503c\u3002 SQL \u4e2d CASE WHEN \u7684\u591a\u79cd\u7528\u6cd5 CASE WHEN \u8bed\u53e5\u5728 SQL \u4e2d\u7528\u4e8e\u6839\u636e\u6307\u5b9a\u7684\u6761\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u503c\u3002\u5b83\u662f\u4e00\u79cd\u5f3a\u5927\u7684\u5de5\u5177\uff0c\u53ef\u4ee5\u6267\u884c\u5404\u79cd\u6570\u636e\u8f6c\u6362\u548c\u67e5\u8be2\u64cd\u4f5c\u3002 \u57fa\u672c\u7528\u6cd5 \u6700\u57fa\u672c\u7684\u5f62\u5f0f\u5982\u4e0b\uff1a CASE WHEN <condition> THEN <value_if_true> ELSE <value_if_false> END \u767b\u5f55\u540e\u590d\u5236 \uff1a \u8981\u8bc4\u4f30\u7684\u6761\u4ef6\u3002 \uff1a \u5982\u679c\u6761\u4ef6\u4e3a true \u65f6\u8981\u8fd4\u56de\u7684\u503c\u3002 \uff1a \u5982\u679c\u6761\u4ef6\u4e3a false \u65f6\u8981\u8fd4\u56de\u7684\u503c\u3002 \u591a\u91cd\u6761\u4ef6 CASE WHEN \u8bed\u53e5\u53ef\u4ee5\u5904\u7406\u591a\u4e2a\u6761\u4ef6\uff0c\u5982\u4e0b\u6240\u793a\uff1a CASE WHEN <condition1> THEN <value_if_true1> WHEN <condition2> THEN <value_if_true2> … ELSE <value_if_no_match> END \u767b\u5f55\u540e\u590d\u5236 \u641c\u7d22\u7279\u5b9a\u503c […]<\/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-5202","post","type-post","status-publish","format-standard","hentry","category-16"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/5202","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=5202"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/5202\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=5202"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=5202"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=5202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}