{"id":168509,"date":"2024-11-06T12:58:25","date_gmt":"2024-11-06T04:58:25","guid":{"rendered":"https:\/\/server.hk\/cnblog\/168509\/"},"modified":"2024-11-06T12:58:26","modified_gmt":"2024-11-06T04:58:26","slug":"sql-%e4%b8%ad-substring-%e7%9a%84%e8%aa%9e%e6%b3%95%e8%aa%aa%e6%98%8e","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/168509\/","title":{"rendered":"SQL \u4e2d SUBSTRING \u7684\u8a9e\u6cd5\u8aaa\u660e"},"content":{"rendered":"<h1 id=\"sql-%e4%b8%ad-substring-%e7%9a%84%e8%aa%9e%e6%b3%95%e8%aa%aa%e6%98%8e-LjvnCqlaLh\">SQL \u4e2d SUBSTRING \u7684\u8a9e\u6cd5\u8aaa\u660e<\/h1>\n<p>\u5728 SQL \u4e2d\uff0cSUBSTRING \u51fd\u6578\u662f\u4e00\u500b\u975e\u5e38\u6709\u7528\u7684\u5b57\u7b26\u4e32\u8655\u7406\u51fd\u6578\uff0c\u80fd\u5920\u5f9e\u4e00\u500b\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u51fa\u6307\u5b9a\u7684\u5b50\u5b57\u7b26\u4e32\u3002\u9019\u5728\u6578\u64da\u5eab\u67e5\u8a62\u548c\u6578\u64da\u8655\u7406\u4e2d\u7d93\u5e38\u88ab\u4f7f\u7528\uff0c\u7279\u5225\u662f\u5728\u9700\u8981\u5c0d\u5b57\u7b26\u4e32\u9032\u884c\u5206\u6790\u6216\u683c\u5f0f\u5316\u7684\u60c5\u6cc1\u4e0b\u3002\u672c\u6587\u5c07\u8a73\u7d30\u4ecb\u7d39 SQL \u4e2d SUBSTRING \u7684\u8a9e\u6cd5\u53ca\u5176\u4f7f\u7528\u65b9\u6cd5\u3002<\/p>\n<h2 id=\"substring-%e5%87%bd%e6%95%b8%e7%9a%84%e5%9f%ba%e6%9c%ac%e8%aa%9e%e6%b3%95-LjvnCqlaLh\">SUBSTRING \u51fd\u6578\u7684\u57fa\u672c\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\u5f9e\u4e2d\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\u8d77\u59cb\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\u5982\u679c\u7701\u7565\uff0c\u5247\u63d0\u53d6\u5230\u5b57\u7b26\u4e32\u7684\u7d50\u5c3e\u3002<\/li>\n<\/ul>\n<h2 id=\"%e4%bd%bf%e7%94%a8%e7%af%84%e4%be%8b-LjvnCqlaLh\">\u4f7f\u7528\u7bc4\u4f8b<\/h2>\n<p>\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4f7f\u7528 SUBSTRING \u51fd\u6578\u7684\u7bc4\u4f8b\uff1a<\/p>\n<h3 id=\"%e7%af%84%e4%be%8b-1%ef%bc%9a%e5%9f%ba%e6%9c%ac%e4%bd%bf%e7%94%a8-LjvnCqlaLh\">\u7bc4\u4f8b 1\uff1a\u57fa\u672c\u4f7f\u7528<\/h3>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba <code>employees<\/code> \u7684\u8868\u683c\uff0c\u5176\u4e2d\u6709\u4e00\u500b <code>name<\/code> \u6b04\u4f4d\uff0c\u5305\u542b\u54e1\u5de5\u7684\u5168\u540d\u3002\u6211\u5011\u60f3\u8981\u63d0\u53d6\u6bcf\u4f4d\u54e1\u5de5\u7684\u540d\u5b57\u7684\u524d 3 \u500b\u5b57\u7b26\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b SQL \u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT SUBSTRING(name, 1, 3) AS first_three_chars FROM employees;<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de\u6bcf\u4f4d\u54e1\u5de5\u540d\u5b57\u7684\u524d\u4e09\u500b\u5b57\u7b26\u3002<\/p>\n<h3 id=\"%e7%af%84%e4%be%8b-2%ef%bc%9a%e6%8f%90%e5%8f%96%e5%ad%90%e5%ad%97%e7%ac%a6%e4%b8%b2%e5%88%b0%e7%b5%90%e5%b0%be-LjvnCqlaLh\">\u7bc4\u4f8b 2\uff1a\u63d0\u53d6\u5b50\u5b57\u7b26\u4e32\u5230\u7d50\u5c3e<\/h3>\n<p>\u5982\u679c\u6211\u5011\u60f3\u8981\u63d0\u53d6\u5f9e\u67d0\u500b\u4f4d\u7f6e\u958b\u59cb\u5230\u5b57\u7b26\u4e32\u7d50\u5c3e\u7684\u6240\u6709\u5b57\u7b26\uff0c\u53ef\u4ee5\u7701\u7565 <code>length<\/code> \u53c3\u6578\u3002\u4f8b\u5982\uff0c\u63d0\u53d6\u54e1\u5de5\u540d\u5b57\u7684\u7b2c 4 \u500b\u5b57\u7b26\u5230\u7d50\u5c3e\uff1a<\/p>\n<pre><code>SELECT SUBSTRING(name, 4) AS from_fourth_char FROM employees;<\/code><\/pre>\n<p>\u9019\u5c07\u8fd4\u56de\u6bcf\u4f4d\u54e1\u5de5\u540d\u5b57\u5f9e\u7b2c\u56db\u500b\u5b57\u7b26\u958b\u59cb\u7684\u6240\u6709\u5b57\u7b26\u3002<\/p>\n<h3 id=\"%e7%af%84%e4%be%8b-3%ef%bc%9a%e8%99%95%e7%90%86%e4%b8%8d%e5%90%8c%e7%9a%84%e5%ad%97%e7%ac%a6%e4%b8%b2-LjvnCqlaLh\">\u7bc4\u4f8b 3\uff1a\u8655\u7406\u4e0d\u540c\u7684\u5b57\u7b26\u4e32<\/h3>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u5b57\u7b26\u4e32 <code>'Hello, World!'<\/code>\uff0c\u6211\u5011\u60f3\u8981\u63d0\u53d6 <code>'World'<\/code> \u9019\u500b\u55ae\u8a5e\uff0c\u53ef\u4ee5\u9019\u6a23\u505a\uff1a<\/p>\n<pre><code>SELECT SUBSTRING('Hello, World!', 8, 5) AS extracted_word;<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de <code>'World'<\/code>\uff0c\u56e0\u70ba\u5b83\u5f9e\u7b2c 8 \u500b\u5b57\u7b26\u958b\u59cb\uff0c\u63d0\u53d6 5 \u500b\u5b57\u7b26\u3002<\/p>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-LjvnCqlaLh\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<ul>\n<li>\u5728 SQL \u4e2d\uff0c\u5b57\u7b26\u4e32\u7684\u7d22\u5f15\u662f\u5f9e 1 \u958b\u59cb\u7684\uff0c\u800c\u4e0d\u662f\u5f9e 0 \u958b\u59cb\u3002<\/li>\n<li>\u5982\u679c <code>start<\/code> \u7684\u503c\u5927\u65bc\u5b57\u7b26\u4e32\u7684\u9577\u5ea6\uff0c\u5247\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<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-LjvnCqlaLh\">\u7e3d\u7d50<\/h2>\n<p>SUBSTRING \u51fd\u6578\u5728 SQL \u4e2d\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\u5206\u6790\u5b57\u7b26\u4e32\u6578\u64da\u3002\u7121\u8ad6\u662f\u5728\u6578\u64da\u67e5\u8a62\u9084\u662f\u6578\u64da\u6e05\u7406\u7684\u904e\u7a0b\u4e2d\uff0c\u638c\u63e1 SUBSTRING \u7684\u4f7f\u7528\u65b9\u6cd5\u90fd\u80fd\u63d0\u9ad8\u5de5\u4f5c\u6548\u7387\u3002\u5c0d\u65bc\u9700\u8981\u9ad8\u6548\u6578\u64da\u8655\u7406\u7684\u7528\u6236\uff0c\u9078\u64c7\u5408\u9069\u7684 <a href=\"https:\/\/server.hk\">VPS<\/a> \u89e3\u6c7a\u65b9\u6848\u53ef\u4ee5\u63d0\u4f9b\u66f4\u597d\u7684\u6027\u80fd\u548c\u9748\u6d3b\u6027\uff0c\u7279\u5225\u662f\u5728\u9999\u6e2f\u5730\u5340\u7684\u6578\u64da\u9700\u6c42\u4e0a\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3 SQL \u4e2d SUBSTRING \u51fd\u6578\u7684\u8a9e\u6cd5\uff0c\u5b78\u7fd2\u5982\u4f55\u63d0\u53d6\u5b57\u4e32\u7684\u7279\u5b9a\u90e8\u5206\uff0c\u63d0\u5347\u8cc7\u6599\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-168509","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/168509","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=168509"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/168509\/revisions"}],"predecessor-version":[{"id":168510,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/168509\/revisions\/168510"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=168509"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=168509"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=168509"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}