{"id":143821,"date":"2024-11-01T01:32:18","date_gmt":"2024-10-31T17:32:18","guid":{"rendered":"https:\/\/server.hk\/cnblog\/143821\/"},"modified":"2024-11-01T01:32:19","modified_gmt":"2024-10-31T17:32:19","slug":"sql-%e5%87%bd%e6%95%b8%e4%b8%ad%e7%9a%84-substring-%e5%87%bd%e6%95%b8","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/143821\/","title":{"rendered":"SQL \u51fd\u6578\u4e2d\u7684 SUBSTRING \u51fd\u6578"},"content":{"rendered":"<h1 id=\"sql-%e5%87%bd%e6%95%b8%e4%b8%ad%e7%9a%84-substring-%e5%87%bd%e6%95%b8-rDsFLSgKJh\">SQL \u51fd\u6578\u4e2d\u7684 SUBSTRING \u51fd\u6578<\/h1>\n<p>\u5728 SQL \u4e2d\uff0c\u5b57\u7b26\u4e32\u8655\u7406\u662f\u4e00\u500b\u5e38\u898b\u7684\u9700\u6c42\uff0c\u800c SUBSTRING \u51fd\u6578\u5247\u662f\u7528\u65bc\u63d0\u53d6\u5b57\u7b26\u4e32\u7684\u4e00\u90e8\u5206\u3002\u9019\u500b\u51fd\u6578\u5728\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u975e\u5e38\u6709\u7528\uff0c\u5c24\u5176\u662f\u5728\u9700\u8981\u5f9e\u9577\u5b57\u7b26\u4e32\u4e2d\u7372\u53d6\u7279\u5b9a\u4fe1\u606f\u7684\u60c5\u6cc1\u4e0b\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0e SUBSTRING \u51fd\u6578\u7684\u7528\u6cd5\u3001\u8a9e\u6cd5\u53ca\u5176\u61c9\u7528\u793a\u4f8b\u3002<\/p>\n<h2 id=\"substring-%e5%87%bd%e6%95%b8%e7%9a%84%e8%aa%9e%e6%b3%95-rDsFLSgKJh\">SUBSTRING \u51fd\u6578\u7684\u8a9e\u6cd5<\/h2>\n<p>SUBSTRING \u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>SUBSTRING(string, start, length)<\/code><\/pre>\n<ul>\n<li><strong>string<\/strong>\uff1a\u8981\u63d0\u53d6\u5b50\u5b57\u7b26\u4e32\u7684\u539f\u59cb\u5b57\u7b26\u4e32\u3002<\/li>\n<li><strong>start<\/strong>\uff1a\u958b\u59cb\u63d0\u53d6\u7684\u4f4d\u7f6e\uff0c\u5f9e 1 \u958b\u59cb\u8a08\u7b97\u3002<\/li>\n<li><strong>length<\/strong>\uff1a\u8981\u63d0\u53d6\u7684\u5b57\u7b26\u6578\u3002<\/li>\n<\/ul>\n<p>\u4f8b\u5982\uff0c\u5982\u679c\u6211\u5011\u6709\u4e00\u500b\u5b57\u7b26\u4e32 &#8220;Hello, World!&#8221;\uff0c\u4e26\u5e0c\u671b\u63d0\u53d6 &#8220;World&#8221;\uff0c\u6211\u5011\u53ef\u4ee5\u9019\u6a23\u4f7f\u7528 SUBSTRING \u51fd\u6578\uff1a<\/p>\n<pre><code>SELECT SUBSTRING('Hello, World!', 8, 5); -- \u7d50\u679c\u70ba 'World'<\/code><\/pre>\n<h2 id=\"substring-%e5%87%bd%e6%95%b8%e7%9a%84%e6%87%89%e7%94%a8-rDsFLSgKJh\">SUBSTRING \u51fd\u6578\u7684\u61c9\u7528<\/h2>\n<p>SUBSTRING \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<h3 id=\"1-%e6%8f%90%e5%8f%96%e7%94%a8%e6%88%b6%e5%90%8d-rDsFLSgKJh\">1. \u63d0\u53d6\u7528\u6236\u540d<\/h3>\n<p>\u5728\u4e00\u500b\u7528\u6236\u8cc7\u6599\u8868\u4e2d\uff0c\u5047\u8a2d\u7528\u6236\u7684\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\u5b58\u5132\u5728\u4e00\u500b\u5b57\u6bb5\u4e2d\uff0c\u6211\u5011\u53ef\u80fd\u9700\u8981\u63d0\u53d6\u7528\u6236\u540d\u90e8\u5206\u3002\u5047\u8a2d\u96fb\u5b50\u90f5\u4ef6\u683c\u5f0f\u70ba &#8220;username@example.com&#8221;\uff0c\u6211\u5011\u53ef\u4ee5\u4f7f\u7528 SUBSTRING \u51fd\u6578\u4f86\u7372\u53d6\u7528\u6236\u540d\uff1a<\/p>\n<pre><code>SELECT SUBSTRING(email, 1, CHARINDEX('@', email) - 1) AS username FROM users;<\/code><\/pre>\n<h3 id=\"2-%e6%a0%bc%e5%bc%8f%e5%8c%96%e6%95%b8%e6%93%9a-rDsFLSgKJh\">2. \u683c\u5f0f\u5316\u6578\u64da<\/h3>\n<p>\u5728\u6578\u64da\u5831\u544a\u4e2d\uff0c\u53ef\u80fd\u9700\u8981\u5c07\u67d0\u4e9b\u5b57\u6bb5\u683c\u5f0f\u5316\u70ba\u7279\u5b9a\u7684\u6a23\u5f0f\u3002\u4f8b\u5982\uff0c\u5f9e\u4e00\u500b\u5305\u542b\u5b8c\u6574\u5730\u5740\u7684\u5b57\u6bb5\u4e2d\u63d0\u53d6\u57ce\u5e02\u540d\u7a31\uff1a<\/p>\n<pre><code>SELECT SUBSTRING(address, 1, 10) AS city FROM addresses;<\/code><\/pre>\n<h3 id=\"3-%e6%95%b8%e6%93%9a%e6%b8%85%e7%90%86-rDsFLSgKJh\">3. \u6578\u64da\u6e05\u7406<\/h3>\n<p>\u5728\u6578\u64da\u6e05\u7406\u904e\u7a0b\u4e2d\uff0cSUBSTRING \u51fd\u6578\u53ef\u4ee5\u5e6b\u52a9\u6211\u5011\u5f9e\u4e0d\u898f\u5247\u7684\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u6709\u7528\u7684\u4fe1\u606f\u3002\u4f8b\u5982\uff0c\u5f9e\u4e00\u500b\u5305\u542b\u65e5\u671f\u548c\u6642\u9593\u7684\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u65e5\u671f\u90e8\u5206\uff1a<\/p>\n<pre><code>SELECT SUBSTRING(datetime_column, 1, 10) AS date FROM events;<\/code><\/pre>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-rDsFLSgKJh\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u4f7f\u7528 SUBSTRING \u51fd\u6578\u6642\uff0c\u6709\u5e7e\u9ede\u9700\u8981\u6ce8\u610f\uff1a<\/p>\n<ul>\n<li>\u5982\u679c <code>start<\/code> \u7684\u503c\u5c0f\u65bc 1\uff0c\u5247\u6703\u8fd4\u56de\u7a7a\u5b57\u7b26\u4e32\u3002<\/li>\n<li>\u5982\u679c <code>length<\/code> \u7684\u503c\u70ba\u8ca0\u6578\uff0c\u5247\u6703\u8fd4\u56de\u7a7a\u5b57\u7b26\u4e32\u3002<\/li>\n<li>\u5982\u679c <code>start<\/code> \u7684\u503c\u8d85\u904e\u5b57\u7b26\u4e32\u7684\u9577\u5ea6\uff0c\u5247\u6703\u8fd4\u56de\u7a7a\u5b57\u7b26\u4e32\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b5%90%e8%ab%96-rDsFLSgKJh\">\u7d50\u8ad6<\/h2>\n<p>SUBSTRING \u51fd\u6578\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u53ef\u4ee5\u5e6b\u52a9\u958b\u767c\u8005\u5728 SQL \u67e5\u8a62\u4e2d\u9748\u6d3b\u5730\u8655\u7406\u5b57\u7b26\u4e32\u6578\u64da\u3002\u7121\u8ad6\u662f\u63d0\u53d6\u7528\u6236\u540d\u3001\u683c\u5f0f\u5316\u6578\u64da\u9084\u662f\u9032\u884c\u6578\u64da\u6e05\u7406\uff0cSUBSTRING \u51fd\u6578\u90fd\u80fd\u63d0\u4f9b\u6709\u6548\u7684\u89e3\u6c7a\u65b9\u6848\u3002\u638c\u63e1\u9019\u500b\u51fd\u6578\u7684\u4f7f\u7528\uff0c\u5c07\u6709\u52a9\u65bc\u63d0\u9ad8\u6578\u64da\u8655\u7406\u7684\u6548\u7387\u548c\u6e96\u78ba\u6027\u3002<\/p>\n<p>\u5982\u679c\u60a8\u5c0d\u65bc <a href=\"https:\/\/server.hk\">\u9999\u6e2f VPS<\/a> \u670d\u52d9\u6709\u8208\u8da3\uff0c\u6216\u60f3\u4e86\u89e3\u66f4\u591a\u95dc\u65bc <a href=\"https:\/\/server.hk\">\u4f3a\u670d\u5668<\/a> \u7684\u8cc7\u8a0a\uff0c\u6b61\u8fce\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4ee5\u7372\u53d6\u66f4\u591a\u8a73\u7d30\u8cc7\u6599\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3 SQL \u51fd\u6578\u4e2d\u7684 SUBSTRING \u51fd\u6578\uff0c\u5b78\u7fd2\u5982\u4f55\u63d0\u53d6\u5b57\u4e32\u7684\u7279\u5b9a\u90e8\u5206\uff0c\u63d0\u5347\u6578\u64da\u8655\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-143821","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143821","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=143821"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143821\/revisions"}],"predecessor-version":[{"id":143822,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143821\/revisions\/143822"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=143821"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=143821"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=143821"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}