{"id":78836,"date":"2024-10-16T12:20:17","date_gmt":"2024-10-16T04:20:17","guid":{"rendered":"https:\/\/server.hk\/cnblog\/78836\/"},"modified":"2024-10-16T12:20:17","modified_gmt":"2024-10-16T04:20:17","slug":"mysql%e6%8c%87%e4%bb%a4-isnull%ef%bc%88%e6%98%af%e5%90%a6%e7%82%ba%e7%a9%ba%ef%bc%89","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/78836\/","title":{"rendered":"MySQL\u6307\u4ee4: ISNULL\uff08\u662f\u5426\u70ba\u7a7a\uff09"},"content":{"rendered":"<h1 id=\"mysql%e6%8c%87%e4%bb%a4-isnull%ef%bc%88%e6%98%af%e5%90%a6%e7%82%ba%e7%a9%ba%ef%bc%89-WqBZHMztpv\">MySQL\u6307\u4ee4: ISNULL\uff08\u662f\u5426\u70ba\u7a7a\uff09<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0c\u8655\u7406\u7a7a\u503c\u662f\u4e00\u500b\u5e38\u898b\u7684\u9700\u6c42\u3002MySQL\u63d0\u4f9b\u4e86\u591a\u7a2e\u65b9\u6cd5\u4f86\u6aa2\u67e5\u548c\u8655\u7406\u7a7a\u503c\uff0c\u5176\u4e2d\u6700\u5e38\u7528\u7684\u6307\u4ee4\u4e4b\u4e00\u5c31\u662fISNULL\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eISNULL\u6307\u4ee4\u7684\u7528\u6cd5\u53ca\u5176\u5728\u5be6\u969b\u61c9\u7528\u4e2d\u7684\u91cd\u8981\u6027\u3002<\/p>\n<h2 id=\"isnull%e6%8c%87%e4%bb%a4%e6%a6%82%e8%bf%b0-WqBZHMztpv\">ISNULL\u6307\u4ee4\u6982\u8ff0<\/h2>\n<p>ISNULL\u662f\u4e00\u500b\u7528\u65bc\u6aa2\u67e5\u67d0\u500b\u8868\u9054\u5f0f\u662f\u5426\u70baNULL\u7684\u51fd\u6578\u3002\u7576\u8868\u9054\u5f0f\u70baNULL\u6642\uff0cISNULL\u8fd4\u56de1\uff08\u771f\uff09\uff0c\u5426\u5247\u8fd4\u56de0\uff08\u5047\uff09\u3002\u9019\u5728\u6578\u64da\u67e5\u8a62\u548c\u6578\u64da\u8655\u7406\u4e2d\u975e\u5e38\u6709\u7528\uff0c\u7279\u5225\u662f\u5728\u9700\u8981\u7be9\u9078\u6216\u8655\u7406\u7a7a\u503c\u7684\u60c5\u6cc1\u4e0b\u3002<\/p>\n<h2 id=\"isnull%e7%9a%84%e5%9f%ba%e6%9c%ac%e8%aa%9e%e6%b3%95-WqBZHMztpv\">ISNULL\u7684\u57fa\u672c\u8a9e\u6cd5<\/h2>\n<pre><code>ISNULL(expression)<\/code><\/pre>\n<p>\u5728\u9019\u88e1\uff0c<code>expression<\/code>\u53ef\u4ee5\u662f\u4efb\u4f55\u6578\u64da\u985e\u578b\u7684\u503c\u6216\u5217\u540d\u3002\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4f7f\u7528ISNULL\u7684\u7bc4\u4f8b\uff1a<\/p>\n<h3 id=\"%e7%af%84%e4%be%8b1-%e5%9f%ba%e6%9c%ac%e4%bd%bf%e7%94%a8-WqBZHMztpv\">\u7bc4\u4f8b1: \u57fa\u672c\u4f7f\u7528<\/h3>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba<code>employees<\/code>\u7684\u8868\uff0c\u5305\u542b\u4ee5\u4e0b\u6b04\u4f4d\uff1a<\/p>\n<ul>\n<li><code>id<\/code><\/li>\n<li><code>name<\/code><\/li>\n<li><code>email<\/code><\/li>\n<\/ul>\n<p>\u6211\u5011\u60f3\u8981\u67e5\u8a62\u6240\u6709\u96fb\u5b50\u90f5\u4ef6\u70baNULL\u7684\u54e1\u5de5\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0bSQL\u8a9e\u53e5\uff1a<\/p>\n<pre><code>SELECT * FROM employees WHERE ISNULL(email);<\/code><\/pre>\n<p>\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de\u6240\u6709\u96fb\u5b50\u90f5\u4ef6\u6b04\u4f4d\u70baNULL\u7684\u54e1\u5de5\u8a18\u9304\u3002<\/p>\n<h3 id=\"%e7%af%84%e4%be%8b2-%e8%88%87%e5%85%b6%e4%bb%96%e5%87%bd%e6%95%b8%e7%b5%90%e5%90%88%e4%bd%bf%e7%94%a8-WqBZHMztpv\">\u7bc4\u4f8b2: \u8207\u5176\u4ed6\u51fd\u6578\u7d50\u5408\u4f7f\u7528<\/h3>\n<p>ISNULL\u4e5f\u53ef\u4ee5\u8207\u5176\u4ed6\u51fd\u6578\u7d50\u5408\u4f7f\u7528\uff0c\u4ee5\u4fbf\u5728\u67e5\u8a62\u4e2d\u63d0\u4f9b\u66f4\u9748\u6d3b\u7684\u7d50\u679c\u3002\u4f8b\u5982\uff0c\u6211\u5011\u53ef\u4ee5\u4f7f\u7528<code>IF<\/code>\u51fd\u6578\u4f86\u66ff\u63dbNULL\u503c\uff1a<\/p>\n<pre><code>SELECT id, name, IF(ISNULL(email), '\u672a\u63d0\u4f9b', email) AS email_status FROM employees;<\/code><\/pre>\n<p>\u5728\u9019\u500b\u67e5\u8a62\u4e2d\uff0c\u5982\u679c\u96fb\u5b50\u90f5\u4ef6\u70baNULL\uff0c\u5247\u8fd4\u56de\u201c\u672a\u63d0\u4f9b\u201d\uff0c\u5426\u5247\u8fd4\u56de\u5be6\u969b\u7684\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\u3002<\/p>\n<h2 id=\"isnull%e7%9a%84%e6%87%89%e7%94%a8%e5%a0%b4%e6%99%af-WqBZHMztpv\">ISNULL\u7684\u61c9\u7528\u5834\u666f<\/h2>\n<p>ISNULL\u51fd\u6578\u5728\u591a\u7a2e\u60c5\u6cc1\u4e0b\u90fd\u975e\u5e38\u6709\u7528\uff0c\u4ee5\u4e0b\u662f\u4e00\u4e9b\u5e38\u898b\u7684\u61c9\u7528\u5834\u666f\uff1a<\/p>\n<ul>\n<li><strong>\u6578\u64da\u6e05\u7406\uff1a<\/strong>\u5728\u6578\u64da\u9077\u79fb\u6216\u6574\u5408\u904e\u7a0b\u4e2d\uff0cISNULL\u53ef\u4ee5\u5e6b\u52a9\u8b58\u5225\u548c\u8655\u7406\u7a7a\u503c\u3002<\/li>\n<li><strong>\u5831\u544a\u751f\u6210\uff1a<\/strong>\u5728\u751f\u6210\u5831\u544a\u6642\uff0cISNULL\u53ef\u4ee5\u7528\u4f86\u78ba\u4fdd\u5831\u544a\u4e2d\u7684\u6578\u64da\u5b8c\u6574\u6027\uff0c\u907f\u514d\u56e0\u7a7a\u503c\u800c\u5c0e\u81f4\u7684\u932f\u8aa4\u3002<\/li>\n<li><strong>\u689d\u4ef6\u67e5\u8a62\uff1a<\/strong>\u5728\u9032\u884c\u689d\u4ef6\u67e5\u8a62\u6642\uff0cISNULL\u53ef\u4ee5\u5e6b\u52a9\u7be9\u9078\u51fa\u7279\u5b9a\u7684\u6578\u64da\u96c6\u3002<\/li>\n<\/ul>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-WqBZHMztpv\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u5728\u4f7f\u7528ISNULL\u6642\uff0c\u9700\u8981\u6ce8\u610f\u4ee5\u4e0b\u5e7e\u9ede\uff1a<\/p>\n<ul>\n<li>ISNULL\u50c5\u6aa2\u67e5NULL\u503c\uff0c\u5c0d\u65bc\u7a7a\u5b57\u7b26\u4e32\uff08&#8221;\uff09\u6216\u5176\u4ed6\u985e\u578b\u7684\u7a7a\u503c\u4e0d\u6703\u8fd4\u56de\u771f\u3002<\/li>\n<li>\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u4f7f\u7528<code>COALESCE<\/code>\u51fd\u6578\u53ef\u80fd\u66f4\u70ba\u5408\u9069\uff0c\u56e0\u70ba\u5b83\u53ef\u4ee5\u6aa2\u67e5\u591a\u500b\u8868\u9054\u5f0f\u4e26\u8fd4\u56de\u7b2c\u4e00\u500b\u975eNULL\u7684\u503c\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-WqBZHMztpv\">\u7e3d\u7d50<\/h2>\n<p>ISNULL\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u958b\u767c\u8005\u548c\u6578\u64da\u5206\u6790\u5e2b\u6709\u6548\u5730\u8655\u7406\u548c\u6aa2\u67e5\u7a7a\u503c\u3002\u5728\u6578\u64da\u5eab\u64cd\u4f5c\u4e2d\uff0c\u6b63\u78ba\u4f7f\u7528ISNULL\u53ef\u4ee5\u63d0\u9ad8\u67e5\u8a62\u7684\u6e96\u78ba\u6027\u548c\u6548\u7387\u3002\u5c0d\u65bc\u9700\u8981\u9ad8\u6548\u6578\u64da\u8655\u7406\u7684\u7528\u6236\uff0c\u9078\u64c7\u5408\u9069\u7684<code>VPS<\/code>\u89e3\u6c7a\u65b9\u6848\uff0c\u5982<a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a>\uff0c\u53ef\u4ee5\u63d0\u4f9b\u66f4\u597d\u7684\u6027\u80fd\u548c\u7a69\u5b9a\u6027\uff0c\u9032\u4e00\u6b65\u63d0\u5347\u6578\u64da\u5eab\u64cd\u4f5c\u7684\u6548\u7387\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3MySQL\u6307\u4ee4ISNULL\uff0c\u6aa2\u67e5\u6578\u64da\u662f\u5426\u70ba\u7a7a\uff0c\u63d0\u5347\u6578\u64da\u67e5\u8a62\u6548\u7387\uff0c\u78ba\u4fdd\u6578\u64da\u5b8c\u6574\u6027\u8207\u6e96\u78ba\u6027\u3002<\/p>\n","protected":false},"author":0,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-78836","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78836","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"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=78836"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78836\/revisions"}],"predecessor-version":[{"id":78837,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78836\/revisions\/78837"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=78836"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=78836"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=78836"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}