{"id":78910,"date":"2024-10-16T12:27:17","date_gmt":"2024-10-16T04:27:17","guid":{"rendered":"https:\/\/server.hk\/cnblog\/78910\/"},"modified":"2024-10-16T12:27:18","modified_gmt":"2024-10-16T04:27:18","slug":"mysql%e6%8c%87%e4%bb%a4-left%ef%bc%88%e5%b7%a6%e6%88%aa%e5%8f%96%ef%bc%89","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/78910\/","title":{"rendered":"MySQL\u6307\u4ee4: LEFT()\uff08\u5de6\u622a\u53d6\uff09"},"content":{"rendered":"<h1 id=\"mysql%e6%8c%87%e4%bb%a4-left%ef%bc%88%e5%b7%a6%e6%88%aa%e5%8f%96%ef%bc%89-HOdnDSYISK\">MySQL\u6307\u4ee4: LEFT()\uff08\u5de6\u622a\u53d6\uff09<\/h1>\n<p>\u5728\u8cc7\u6599\u5eab\u7ba1\u7406\u4e2d\uff0cMySQL\u662f\u4e00\u500b\u5ee3\u6cdb\u4f7f\u7528\u7684\u95dc\u806f\u5f0f\u8cc7\u6599\u5eab\u7ba1\u7406\u7cfb\u7d71\u3002\u5b83\u63d0\u4f9b\u4e86\u591a\u7a2e\u529f\u80fd\u5f37\u5927\u7684\u6307\u4ee4\u4f86\u8655\u7406\u548c\u64cd\u4f5c\u6578\u64da\u3002\u5176\u4e2d\uff0cLEFT()\u51fd\u6578\u662f\u4e00\u500b\u975e\u5e38\u5be6\u7528\u7684\u5b57\u7b26\u4e32\u51fd\u6578\uff0c\u80fd\u5920\u5f9e\u4e00\u500b\u5b57\u7b26\u4e32\u7684\u5de6\u5074\u622a\u53d6\u6307\u5b9a\u6578\u91cf\u7684\u5b57\u7b26\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eLEFT()\u51fd\u6578\u7684\u7528\u6cd5\u53ca\u5176\u61c9\u7528\u5834\u666f\u3002<\/p>\n<h2 id=\"left%e5%87%bd%e6%95%b8%e7%9a%84%e5%9f%ba%e6%9c%ac%e8%aa%9e%e6%b3%95-HOdnDSYISK\">LEFT()\u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5<\/h2>\n<p>LEFT()\u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>LEFT(string, length)<\/code><\/pre>\n<ul>\n<li><strong>string<\/strong>: \u8981\u9032\u884c\u622a\u53d6\u7684\u5b57\u7b26\u4e32\u3002<\/li>\n<li><strong>length<\/strong>: \u8981\u622a\u53d6\u7684\u5b57\u7b26\u6578\u91cf\u3002<\/li>\n<\/ul>\n<p>\u9019\u500b\u51fd\u6578\u6703\u8fd4\u56de\u5f9e\u5b57\u7b26\u4e32\u7684\u5de6\u5074\u958b\u59cb\u7684\u6307\u5b9a\u6578\u91cf\u7684\u5b57\u7b26\u3002\u5982\u679c\u6307\u5b9a\u7684\u9577\u5ea6\u8d85\u904e\u4e86\u5b57\u7b26\u4e32\u7684\u5be6\u969b\u9577\u5ea6\uff0c\u5247\u8fd4\u56de\u6574\u500b\u5b57\u7b26\u4e32\u3002<\/p>\n<h2 id=\"%e4%bd%bf%e7%94%a8%e7%af%84%e4%be%8b-HOdnDSYISK\">\u4f7f\u7528\u7bc4\u4f8b<\/h2>\n<p>\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4f7f\u7528LEFT()\u51fd\u6578\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-HOdnDSYISK\">\u7bc4\u4f8b1: \u57fa\u672c\u4f7f\u7528<\/h3>\n<pre><code>SELECT LEFT('Hello, World!', 5) AS Result;<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de\u201cHello\u201d\uff0c\u56e0\u70ba\u5b83\u5f9e\u5b57\u7b26\u4e32\u201cHello, World!\u201d\u7684\u5de6\u5074\u622a\u53d6\u4e865\u500b\u5b57\u7b26\u3002<\/p>\n<h3 id=\"%e7%af%84%e4%be%8b2-%e8%b6%85%e9%81%8e%e5%ad%97%e7%ac%a6%e4%b8%b2%e9%95%b7%e5%ba%a6-HOdnDSYISK\">\u7bc4\u4f8b2: \u8d85\u904e\u5b57\u7b26\u4e32\u9577\u5ea6<\/h3>\n<pre><code>SELECT LEFT('MySQL', 10) AS Result;<\/code><\/pre>\n<p>\u5728\u9019\u500b\u4f8b\u5b50\u4e2d\uff0c\u56e0\u70ba\u201cMySQL\u201d\u7684\u9577\u5ea6\u53ea\u67095\u500b\u5b57\u7b26\uff0c\u6240\u4ee5\u8fd4\u56de\u7684\u7d50\u679c\u4ecd\u7136\u662f\u201cMySQL\u201d\u3002<\/p>\n<h3 id=\"%e7%af%84%e4%be%8b3-%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-HOdnDSYISK\">\u7bc4\u4f8b3: \u8207\u5176\u4ed6\u51fd\u6578\u7d50\u5408\u4f7f\u7528<\/h3>\n<p>LEFT()\u51fd\u6578\u53ef\u4ee5\u8207\u5176\u4ed6\u5b57\u7b26\u4e32\u51fd\u6578\u7d50\u5408\u4f7f\u7528\uff0c\u4ee5\u9054\u5230\u66f4\u8907\u96dc\u7684\u64cd\u4f5c\u3002\u4f8b\u5982\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u5305\u542b\u7528\u6236\u96fb\u5b50\u90f5\u4ef6\u7684\u8868\u683c\uff0c\u6211\u5011\u60f3\u8981\u63d0\u53d6\u7528\u6236\u540d\u90e8\u5206\uff1a<\/p>\n<pre><code>SELECT LEFT(email, LOCATE('@', email) - 1) AS Username FROM users;<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de\u7528\u6236\u96fb\u5b50\u90f5\u4ef6\u4e2d\u7684\u7528\u6236\u540d\u90e8\u5206\uff0c\u901a\u904e\u67e5\u627e\u201c@\u201d\u7b26\u865f\u7684\u4f4d\u7f6e\u4f86\u78ba\u5b9a\u622a\u53d6\u7684\u9577\u5ea6\u3002<\/p>\n<h2 id=\"%e6%87%89%e7%94%a8%e5%a0%b4%e6%99%af-HOdnDSYISK\">\u61c9\u7528\u5834\u666f<\/h2>\n<p>LEFT()\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<\/strong>: \u5728\u6578\u64da\u5c0e\u5165\u904e\u7a0b\u4e2d\uff0c\u53ef\u80fd\u6703\u9047\u5230\u4e0d\u5fc5\u8981\u7684\u524d\u7db4\u6216\u5f8c\u7db4\uff0c\u4f7f\u7528LEFT()\u51fd\u6578\u53ef\u4ee5\u8f15\u9b06\u6e05\u7406\u9019\u4e9b\u6578\u64da\u3002<\/li>\n<li><strong>\u5831\u544a\u751f\u6210<\/strong>: \u5728\u751f\u6210\u5831\u544a\u6642\uff0c\u53ef\u80fd\u9700\u8981\u986f\u793a\u67d0\u4e9b\u5b57\u6bb5\u7684\u90e8\u5206\u5167\u5bb9\uff0cLEFT()\u51fd\u6578\u53ef\u4ee5\u5e6b\u52a9\u63d0\u53d6\u6240\u9700\u7684\u5b57\u7b26\u3002<\/li>\n<li><strong>\u7528\u6236\u754c\u9762\u986f\u793a<\/strong>: \u5728\u7528\u6236\u754c\u9762\u4e2d\uff0c\u986f\u793a\u9577\u5b57\u7b26\u4e32\u6642\uff0c\u4f7f\u7528LEFT()\u51fd\u6578\u53ef\u4ee5\u9650\u5236\u986f\u793a\u7684\u5b57\u7b26\u6578\uff0c\u63d0\u5347\u53ef\u8b80\u6027\u3002<\/li>\n<\/ul>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-HOdnDSYISK\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u5728\u4f7f\u7528LEFT()\u51fd\u6578\u6642\uff0c\u6709\u5e7e\u9ede\u9700\u8981\u6ce8\u610f\uff1a<\/p>\n<ul>\n<li>\u5982\u679clength\u70ba\u8ca0\u6578\uff0c\u5247LEFT()\u51fd\u6578\u5c07\u8fd4\u56deNULL\u3002<\/li>\n<li>\u5982\u679cstring\u70baNULL\uff0c\u5247\u8fd4\u56de\u7684\u7d50\u679c\u4e5f\u5c07\u662fNULL\u3002<\/li>\n<li>LEFT()\u51fd\u6578\u4e0d\u6703\u6539\u8b8a\u539f\u59cb\u5b57\u7b26\u4e32\uff0c\u5b83\u50c5\u50c5\u662f\u8fd4\u56de\u4e00\u500b\u65b0\u7684\u5b57\u7b26\u4e32\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-HOdnDSYISK\">\u7e3d\u7d50<\/h2>\n<p>LEFT()\u51fd\u6578\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u958b\u767c\u8005\u5728MySQL\u4e2d\u6709\u6548\u5730\u8655\u7406\u5b57\u7b26\u4e32\u6578\u64da\u3002\u7121\u8ad6\u662f\u5728\u6578\u64da\u6e05\u7406\u3001\u5831\u544a\u751f\u6210\u9084\u662f\u7528\u6236\u754c\u9762\u986f\u793a\u65b9\u9762\uff0cLEFT()\u51fd\u6578\u90fd\u80fd\u767c\u63ee\u91cd\u8981\u4f5c\u7528\u3002\u5c0d\u65bc\u9700\u8981\u9ad8\u6548\u7ba1\u7406\u6578\u64da\u7684\u4f01\u696d\u4f86\u8aaa\uff0c\u638c\u63e1\u9019\u4e9b\u57fa\u672c\u7684MySQL\u6307\u4ee4\u662f\u975e\u5e38\u5fc5\u8981\u7684\u3002\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u7a69\u5b9a\u7684 <a href=\"https:\/\/server.hk\">VPS<\/a> \u89e3\u6c7a\u65b9\u6848\u4f86\u904b\u884c\u60a8\u7684\u6578\u64da\u5eab\uff0cServer.HK\u63d0\u4f9b\u4e86\u591a\u7a2e\u9078\u64c7\uff0c\u6eff\u8db3\u4e0d\u540c\u9700\u6c42\u7684\u5ba2\u6236\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3MySQL\u7684LEFT()\u51fd\u6570\uff0c\u8f7b\u677e\u622a\u53d6\u5b57\u7b26\u4e32\u5de6\u4fa7\u6307\u5b9a\u957f\u5ea6\u7684\u5b57\u7b26\uff0c\u63d0\u5347\u6570\u636e\u5904\u7406\u6548\u7387\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-78910","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78910","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=78910"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78910\/revisions"}],"predecessor-version":[{"id":78911,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78910\/revisions\/78911"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=78910"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=78910"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=78910"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}