{"id":199744,"date":"2025-05-06T09:43:26","date_gmt":"2025-05-06T01:43:26","guid":{"rendered":"https:\/\/server.hk\/cnblog\/199744\/"},"modified":"2025-05-06T09:43:26","modified_gmt":"2025-05-06T01:43:26","slug":"mysql%e4%b8%ad%e7%9a%84isnull%e5%87%bd%e6%95%b0%e7%94%a8%e6%b3%95%e5%8f%8a%e8%af%a6%e8%a7%a3","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/199744\/","title":{"rendered":"MySQL\u4e2d\u7684ISNULL\u51fd\u6570\u7528\u6cd5\u53ca\u8be6\u89e3"},"content":{"rendered":"

<\/b> <\/p>\n

MySQL\u4e2d\u7684ISNULL\u51fd\u6570\u7528\u6cd5\u53ca\u8be6\u89e3<\/h1>\n

\u4eca\u65e5\u4e0d\u80af\u57cb\u5934\uff0c\u660e\u65e5\u4f55\u4ee5\u62ac\u5934\uff01\u6bcf\u65e5\u4e00\u53e5\u52aa\u529b\u81ea\u5df1\u7684\u8bdd\u54c8\u54c8~\u54c8\u55bd\uff0c\u4eca\u5929\u6211\u5c06\u7ed9\u5927\u5bb6\u5e26\u6765\u4e00\u7bc7\uff0c\u4e3b\u8981\u5185\u5bb9\u662f\u8bb2\u89e3\u7b49\u7b49\uff0c\u611f\u5174\u8da3\u7684\u670b\u53cb\u53ef\u4ee5\u6536\u85cf\u6216\u8005\u6709\u66f4\u597d\u7684\u5efa\u8bae\u5728\u8bc4\u8bba\u63d0\u51fa\uff0c\u6211\u90fd\u4f1a\u8ba4\u771f\u770b\u7684\uff01\u5927\u5bb6\u4e00\u8d77\u8fdb\u6b65\uff0c\u4e00\u8d77\u5b66\u4e60\uff01<\/p>\n

MySQL\u4e2d\u7684ISNULL()\u51fd\u6570\u662f\u7528\u4e8e\u5224\u65ad\u6307\u5b9a\u8868\u8fbe\u5f0f\u6216\u5217\u662f\u5426\u4e3aNULL\u7684\u51fd\u6570\u3002\u5b83\u8fd4\u56de\u4e00\u4e2a\u5e03\u5c14\u503c\uff0c\u5982\u679c\u8868\u8fbe\u5f0f\u4e3aNULL\u5219\u8fd4\u56de1\uff0c\u5426\u5219\u8fd4\u56de0\u3002ISNULL()\u51fd\u6570\u53ef\u4ee5\u5728SELECT\u8bed\u53e5\u4e2d\u4f7f\u7528\uff0c\u4e5f\u53ef\u4ee5\u5728WHERE\u5b50\u53e5\u4e2d\u8fdb\u884c\u6761\u4ef6\u5224\u65ad\u3002<\/p>\n

1. ISNULL()\u51fd\u6570\u7684\u57fa\u672c\u8bed\u6cd5\uff1a<\/strong><\/p>\n

ISNULL(expression)<\/pre>\n
\u5176\u4e2d\uff0cexpression\u662f\u8981\u5224\u65ad\u662f\u5426\u4e3aNULL\u7684\u8868\u8fbe\u5f0f\u6216\u5217\u3002<\/p>\n
2. \u4f7f\u7528ISNULL()\u51fd\u6570\u7684\u5e38\u89c1\u60c5\u51b5\uff1a<\/strong><\/p>\n
\u793a\u4f8b1\uff1a\u5728SELECT\u8bed\u53e5\u4e2d\u4f7f\u7528ISNULL()\u51fd\u6570<\/strong><\/p>\n
\u5047\u8bbe\u6709\u4e00\u4e2a\u540d\u4e3astudents\u7684\u5b66\u751f\u8868\uff0c\u5176\u4e2d\u5305\u542bid\u3001name\u548cage\u4e09\u5217\uff0c\u6211\u4eec\u60f3\u8981\u67e5\u8be2\u51fa\u6240\u6709\u5e74\u9f84\u4e3aNULL\u7684\u5b66\u751f\u8bb0\u5f55\uff0c\u53ef\u4ee5\u4f7f\u7528\u5982\u4e0bSQL\u8bed\u53e5\uff1a<\/p>\n
SELECT * FROM students WHERE ISNULL(age);<\/pre>\n
\u8be5SQL\u8bed\u53e5\u4e2d\u7684ISNULL(age)\u4f1a\u5224\u65adage\u5217\u662f\u5426\u4e3aNULL\uff0c\u5982\u679c\u4e3aNULL\uff0c\u5219\u8fd4\u56de\u5bf9\u5e94\u7684\u8bb0\u5f55\u3002<\/p>\n
\u793a\u4f8b2\uff1a\u66f4\u65b0\u5217\u503c\u4e3aNULL\u7684\u8bb0\u5f55<\/strong><\/p>\n
\u5982\u679c\u6211\u4eec\u60f3\u8981\u5c06age\u5217\u4e3aNULL\u7684\u8bb0\u5f55\u7684\u5e74\u9f84\u6539\u4e3a18\u5c81\uff0c\u53ef\u4ee5\u4f7f\u7528\u5982\u4e0bUPDATE\u8bed\u53e5\uff1a<\/p>\n
UPDATE students SET age = IF(ISNULL(age), 18, age);<\/pre>\n
\u8be5UPDATE\u8bed\u53e5\u4e2d\u4f7f\u7528\u4e86ISNULL()\u51fd\u6570\u6765\u5224\u65adage\u5217\u662f\u5426\u4e3aNULL\uff0c\u5982\u679c\u4e3aNULL\u5219\u5c06\u5e74\u9f84\u8bbe\u4e3a18\u5c81\uff0c\u5426\u5219\u4fdd\u6301\u539f\u6765\u7684\u503c\u3002<\/p>\n
3. ISNULL()\u51fd\u6570\u7684\u9ad8\u7ea7\u7528\u6cd5\uff1a<\/strong><\/p>\n
\u793a\u4f8b3\uff1a\u4f7f\u7528ISNULL()\u51fd\u6570\u8fdb\u884c\u8868\u8fde\u63a5<\/strong><\/p>\n
\u5047\u8bbe\u6709\u4e24\u4e2a\u8868students\u548cscores\uff0c\u5206\u522b\u5b58\u50a8\u5b66\u751f\u4fe1\u606f\u548c\u6210\u7ee9\u4fe1\u606f\uff0c\u6211\u4eec\u60f3\u8981\u67e5\u8be2\u51fa\u6240\u6709\u5e74\u9f84\u4e3aNULL\u7684\u5b66\u751f\u53ca\u5176\u5bf9\u5e94\u7684\u6210\u7ee9\u8bb0\u5f55\uff0c\u53ef\u4ee5\u4f7f\u7528\u5982\u4e0bSQL\u8bed\u53e5\uff1a<\/p>\n
SELECT s.id, s.name, sc.score\nFROM students s\nLEFT JOIN scores sc ON s.id = sc.student_id\nWHERE ISNULL(s.age);<\/pre>\n
\u8be5SQL\u8bed\u53e5\u5229\u7528ISNULL()\u51fd\u6570\u5bf9\u5b66\u751f\u8868\u4e2d\u7684age\u5217\u8fdb\u884c\u5224\u65ad\uff0c\u4ece\u800c\u7b5b\u9009\u51fa\u5e74\u9f84\u4e3aNULL\u7684\u5b66\u751f\u8bb0\u5f55\uff0c\u5e76\u901a\u8fc7LEFT JOIN\u5c06\u5b66\u751f\u8868\u548c\u6210\u7ee9\u8868\u8fdb\u884c\u8fde\u63a5\u3002<\/p>\n
\u901a\u8fc7\u4ee5\u4e0a\u793a\u4f8b\uff0c\u6211\u4eec\u53ef\u4ee5\u770b\u5230ISNULL()\u51fd\u6570\u5728MySQL\u4e2d\u7684\u7075\u6d3b\u5e94\u7528\u3002\u65e0\u8bba\u662f\u5728SELECT\u8bed\u53e5\u4e2d\u7b5b\u9009\u8bb0\u5f55\uff0c\u8fd8\u662f\u5728UPDATE\u8bed\u53e5\u4e2d\u66f4\u65b0\u6570\u636e\uff0c\u5728\u8868\u8fde\u63a5\u65f6\u8fdb\u884c\u6761\u4ef6\u5224\u65ad\uff0cISNULL()\u51fd\u6570\u90fd\u80fd\u591f\u63d0\u4f9b\u5f88\u5927\u7684\u5e2e\u52a9\u3002\u5e0c\u671b\u672c\u6587\u7684\u4ecb\u7ecd\u80fd\u591f\u5e2e\u52a9\u8bfb\u8005\u66f4\u597d\u5730\u7406\u89e3MySQL\u4e2dISNULL()\u51fd\u6570\u7684\u7528\u6cd5\u3002<\/p>\n
\u4eca\u5929\u5173\u4e8e\u300aMySQL\u4e2d\u7684ISNULL\u51fd\u6570\u7528\u6cd5\u53ca\u8be6\u89e3\u300b\u7684\u5185\u5bb9\u4ecb\u7ecd\u5c31\u5230\u6b64\u7ed3\u675f\uff0c\u5982\u679c\u6709\u4ec0\u4e48\u7591\u95ee\u6216\u8005\u5efa\u8bae\uff0c\u53ef\u4ee5\u5728\u4e3b\u673a\u5b9d\u8d1d\u516c\u4f17\u53f7\u4e0b\u591a\u591a\u56de\u590d\u4ea4\u6d41\uff1b\u6587\u4e2d\u82e5\u6709\u4e0d\u6b63\u4e4b\u5904\uff0c\u4e5f\u5e0c\u671b\u56de\u590d\u7559\u8a00\u4ee5\u544a\u77e5\uff01<\/p>\n
\n
\n <\/dt>\n<\/dl>\n","protected":false},"excerpt":{"rendered":"
MySQL\u4e2d\u7684ISNULL\u51fd\u6570\u7528...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-199744","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/199744","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=199744"}],"version-history":[{"count":0,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/199744\/revisions"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=199744"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=199744"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=199744"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}