{"id":74437,"date":"2024-10-15T22:28:15","date_gmt":"2024-10-15T14:28:15","guid":{"rendered":"https:\/\/server.hk\/cnblog\/74437\/"},"modified":"2024-10-15T22:28:16","modified_gmt":"2024-10-15T14:28:16","slug":"mysql-ifnull%e5%87%bd%e6%95%b8%e7%9a%84%e4%bd%bf%e7%94%a8","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/74437\/","title":{"rendered":"MYSQL IFNULL\u51fd\u6578\u7684\u4f7f\u7528"},"content":{"rendered":"<h1 id=\"mysql-ifnull%e5%87%bd%e6%95%b8%e7%9a%84%e4%bd%bf%e7%94%a8-ouuALrRrQC\">MySQL IFNULL\u51fd\u6578\u7684\u4f7f\u7528<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0c\u8655\u7406\u7a7a\u503c\uff08NULL\uff09\u662f\u4e00\u500b\u5e38\u898b\u7684\u6311\u6230\u3002MySQL\u63d0\u4f9b\u4e86\u591a\u7a2e\u51fd\u6578\u4f86\u8655\u7406\u9019\u4e9b\u60c5\u6cc1\uff0c\u5176\u4e2d\u4e4b\u4e00\u5c31\u662fIFNULL\u51fd\u6578\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eIFNULL\u51fd\u6578\u7684\u4f7f\u7528\u65b9\u6cd5\u53ca\u5176\u5728\u5be6\u969b\u61c9\u7528\u4e2d\u7684\u91cd\u8981\u6027\u3002<\/p>\n<h2 id=\"ifnull%e5%87%bd%e6%95%b8%e6%a6%82%e8%bf%b0-ouuALrRrQC\">IFNULL\u51fd\u6578\u6982\u8ff0<\/h2>\n<p>IFNULL\u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>IFNULL(expression, alt_value)<\/code><\/pre>\n<p>\u9019\u500b\u51fd\u6578\u63a5\u53d7\u5169\u500b\u53c3\u6578\uff1a\u7b2c\u4e00\u500b\u662f\u8981\u6aa2\u67e5\u7684\u8868\u9054\u5f0f\uff0c\u7b2c\u4e8c\u500b\u662f\u7576\u7b2c\u4e00\u500b\u53c3\u6578\u70baNULL\u6642\u8fd4\u56de\u7684\u66ff\u4ee3\u503c\u3002\u5982\u679c\u7b2c\u4e00\u500b\u53c3\u6578\u4e0d\u662fNULL\uff0c\u5247\u8fd4\u56de\u8a72\u8868\u9054\u5f0f\u7684\u503c\u3002<\/p>\n<h2 id=\"%e4%bd%bf%e7%94%a8%e5%a0%b4%e6%99%af-ouuALrRrQC\">\u4f7f\u7528\u5834\u666f<\/h2>\n<p>IFNULL\u51fd\u6578\u5728\u591a\u7a2e\u60c5\u6cc1\u4e0b\u90fd\u975e\u5e38\u6709\u7528\uff0c\u4ee5\u4e0b\u662f\u4e00\u4e9b\u5e38\u898b\u7684\u4f7f\u7528\u5834\u666f\uff1a<\/p>\n<ul>\n<li><strong>\u6578\u64da\u5831\u544a\uff1a<\/strong>\u5728\u751f\u6210\u5831\u544a\u6642\uff0c\u53ef\u80fd\u6703\u9047\u5230NULL\u503c\uff0c\u9019\u6703\u5f71\u97ff\u5831\u544a\u7684\u53ef\u8b80\u6027\u3002\u4f7f\u7528IFNULL\u53ef\u4ee5\u5c07NULL\u503c\u66ff\u63db\u70ba\u66f4\u5177\u610f\u7fa9\u7684\u503c\uff0c\u4f8b\u5982\u201c\u7121\u8cc7\u6599\u201d\u3002<\/li>\n<li><strong>\u8a08\u7b97\u7e3d\u548c\uff1a<\/strong>\u5728\u8a08\u7b97\u7e3d\u548c\u6216\u5e73\u5747\u503c\u6642\uff0cNULL\u503c\u53ef\u80fd\u6703\u5c0e\u81f4\u8a08\u7b97\u932f\u8aa4\u3002\u4f7f\u7528IFNULL\u53ef\u4ee5\u78ba\u4fdd\u8a08\u7b97\u7684\u6e96\u78ba\u6027\u3002<\/li>\n<li><strong>\u6578\u64da\u63d2\u5165\uff1a<\/strong>\u5728\u63d2\u5165\u6578\u64da\u6642\uff0cIFNULL\u53ef\u4ee5\u7528\u4f86\u78ba\u4fdd\u67d0\u4e9b\u6b04\u4f4d\u4e0d\u6703\u56e0\u70baNULL\u800c\u5c0e\u81f4\u63d2\u5165\u5931\u6557\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%af%84%e4%be%8b-ouuALrRrQC\">\u7bc4\u4f8b<\/h2>\n<p>\u4ee5\u4e0b\u662f\u4e00\u500b\u4f7f\u7528IFNULL\u51fd\u6578\u7684\u7bc4\u4f8b\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba\u201cemployees\u201d\u7684\u8868\uff0c\u5305\u542b\u201cname\u201d\u548c\u201cbonus\u201d\u5169\u500b\u6b04\u4f4d\uff1a<\/p>\n<pre><code>SELECT name, IFNULL(bonus, 0) AS bonus\nFROM employees;<\/code><\/pre>\n<p>\u5728\u9019\u500b\u67e5\u8a62\u4e2d\uff0c\u5982\u679c\u201cbonus\u201d\u6b04\u4f4d\u7684\u503c\u70baNULL\uff0c\u5247\u6703\u8fd4\u56de0\uff0c\u5426\u5247\u8fd4\u56de\u5be6\u969b\u7684\u734e\u91d1\u6578\u984d\u3002\u9019\u6a23\u53ef\u4ee5\u78ba\u4fdd\u5728\u5831\u544a\u4e2d\u4e0d\u6703\u51fa\u73feNULL\u503c\u3002<\/p>\n<h2 id=\"%e8%88%87%e5%85%b6%e4%bb%96%e5%87%bd%e6%95%b8%e7%9a%84%e6%af%94%e8%bc%83-ouuALrRrQC\">\u8207\u5176\u4ed6\u51fd\u6578\u7684\u6bd4\u8f03<\/h2>\n<p>\u9664\u4e86IFNULL\uff0cMySQL\u9084\u63d0\u4f9b\u4e86\u5176\u4ed6\u985e\u4f3c\u7684\u51fd\u6578\uff0c\u5982COALESCE\u548cNULLIF\u3002\u9019\u4e9b\u51fd\u6578\u5404\u6709\u5176\u7279\u9ede\uff1a<\/p>\n<ul>\n<li><strong>COALESCE\uff1a<\/strong>\u9019\u500b\u51fd\u6578\u53ef\u4ee5\u63a5\u53d7\u591a\u500b\u53c3\u6578\uff0c\u4e26\u8fd4\u56de\u7b2c\u4e00\u500b\u975eNULL\u7684\u503c\u3002\u4f8b\u5982\uff1a<\/li>\n<pre><code>SELECT COALESCE(bonus, commission, 0) AS payment\n    FROM employees;<\/code><\/pre>\n<li><strong>NULLIF\uff1a<\/strong>\u9019\u500b\u51fd\u6578\u7528\u65bc\u6bd4\u8f03\u5169\u500b\u8868\u9054\u5f0f\uff0c\u5982\u679c\u76f8\u7b49\u5247\u8fd4\u56deNULL\uff0c\u5426\u5247\u8fd4\u56de\u7b2c\u4e00\u500b\u8868\u9054\u5f0f\u3002\u4f8b\u5982\uff1a<\/li>\n<pre><code>SELECT NULLIF(bonus, 0) AS bonus\n    FROM employees;<\/code><\/pre>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-ouuALrRrQC\">\u7e3d\u7d50<\/h2>\n<p>IFNULL\u51fd\u6578\u5728MySQL\u4e2d\u662f\u4e00\u500b\u975e\u5e38\u5be6\u7528\u7684\u5de5\u5177\uff0c\u80fd\u5920\u6709\u6548\u5730\u8655\u7406NULL\u503c\uff0c\u63d0\u5347\u6578\u64da\u7684\u53ef\u8b80\u6027\u548c\u8a08\u7b97\u7684\u6e96\u78ba\u6027\u3002\u7121\u8ad6\u662f\u5728\u6578\u64da\u5831\u544a\u3001\u8a08\u7b97\u7e3d\u548c\u9084\u662f\u6578\u64da\u63d2\u5165\u4e2d\uff0cIFNULL\u90fd\u80fd\u767c\u63ee\u91cd\u8981\u4f5c\u7528\u3002\u5c0d\u65bc\u9700\u8981\u8655\u7406\u5927\u91cf\u6578\u64da\u7684\u7528\u6236\u4f86\u8aaa\uff0c\u638c\u63e1\u9019\u4e9b\u51fd\u6578\u7684\u4f7f\u7528\u5c07\u5927\u5927\u63d0\u9ad8\u5de5\u4f5c\u6548\u7387\u3002<\/p>\n<p>\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684 <a href=\"https:\/\/server.hk\">VPS<\/a> \u89e3\u6c7a\u65b9\u6848\uff0cServer.HK\u63d0\u4f9b\u591a\u7a2e\u9078\u64c7\uff0c\u6eff\u8db3\u60a8\u7684\u9700\u6c42\u3002\u7121\u8ad6\u662f <a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a> \u9084\u662f\u5176\u4ed6\u670d\u52d9\uff0c\u6211\u5011\u90fd\u80fd\u70ba\u60a8\u63d0\u4f9b\u7a69\u5b9a\u7684\u652f\u6301\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3MySQL IFNULL\u51fd\u6578\u7684\u7528\u6cd5\uff0c\u8f15\u9b06\u8655\u7406NULL\u503c\uff0c\u63d0\u5347\u6578\u64da\u67e5\u8a62\u7684\u9748\u6d3b\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-74437","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/74437","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=74437"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/74437\/revisions"}],"predecessor-version":[{"id":74438,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/74437\/revisions\/74438"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=74437"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=74437"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=74437"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}