{"id":143903,"date":"2024-11-01T02:13:18","date_gmt":"2024-10-31T18:13:18","guid":{"rendered":"https:\/\/server.hk\/cnblog\/143903\/"},"modified":"2024-11-01T02:13:19","modified_gmt":"2024-10-31T18:13:19","slug":"sql-%e5%88%aa%e9%99%a4%e5%ad%97%e6%ae%b5%e5%8f%8a%e5%88%a4%e6%96%b7%e5%ad%97%e6%ae%b5%e6%98%af%e5%90%a6%e5%ad%98%e5%9c%a8%e7%9a%84%e6%96%b9%e6%b3%95","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/143903\/","title":{"rendered":"SQL \u522a\u9664\u5b57\u6bb5\u53ca\u5224\u65b7\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u7684\u65b9\u6cd5"},"content":{"rendered":"<h1 id=\"sql-%e5%88%aa%e9%99%a4%e5%ad%97%e6%ae%b5%e5%8f%8a%e5%88%a4%e6%96%b7%e5%ad%97%e6%ae%b5%e6%98%af%e5%90%a6%e5%ad%98%e5%9c%a8%e7%9a%84%e6%96%b9%e6%b3%95-LLVVstsxpG\">SQL \u522a\u9664\u5b57\u6bb5\u53ca\u5224\u65b7\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u7684\u65b9\u6cd5<\/h1>\n<p>\u5728\u8cc7\u6599\u5eab\u7ba1\u7406\u4e2d\uff0cSQL\uff08\u7d50\u69cb\u5316\u67e5\u8a62\u8a9e\u8a00\uff09\u662f\u4e00\u7a2e\u7528\u65bc\u64cd\u4f5c\u548c\u67e5\u8a62\u8cc7\u6599\u7684\u6a19\u6e96\u8a9e\u8a00\u3002\u7576\u6211\u5011\u9700\u8981\u5c0d\u8cc7\u6599\u8868\u9032\u884c\u4fee\u6539\u6642\uff0c\u522a\u9664\u5b57\u6bb5\u662f\u4e00\u500b\u5e38\u898b\u7684\u64cd\u4f5c\u3002\u7136\u800c\uff0c\u5728\u522a\u9664\u5b57\u6bb5\u4e4b\u524d\uff0c\u78ba\u8a8d\u8a72\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u662f\u975e\u5e38\u91cd\u8981\u7684\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u5982\u4f55\u5728 SQL \u4e2d\u522a\u9664\u5b57\u6bb5\u4ee5\u53ca\u5982\u4f55\u5224\u65b7\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u7684\u65b9\u6cd5\u3002<\/p>\n<h2 id=\"%e4%b8%80%e3%80%81%e5%88%aa%e9%99%a4%e5%ad%97%e6%ae%b5%e7%9a%84%e5%9f%ba%e6%9c%ac%e8%aa%9e%e6%b3%95-LLVVstsxpG\">\u4e00\u3001\u522a\u9664\u5b57\u6bb5\u7684\u57fa\u672c\u8a9e\u6cd5<\/h2>\n<p>\u5728 SQL \u4e2d\uff0c\u522a\u9664\u5b57\u6bb5\u7684\u64cd\u4f5c\u901a\u5e38\u4f7f\u7528 ALTER TABLE \u8a9e\u53e5\u3002\u5176\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>ALTER TABLE \u8868\u540d DROP COLUMN \u5b57\u6bb5\u540d;<\/code><\/pre>\n<p>\u4f8b\u5982\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba <code>employees<\/code> \u7684\u8cc7\u6599\u8868\uff0c\u4e26\u4e14\u6211\u5011\u60f3\u8981\u522a\u9664 <code>age<\/code> \u9019\u500b\u5b57\u6bb5\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b SQL \u8a9e\u53e5\uff1a<\/p>\n<pre><code>ALTER TABLE employees DROP COLUMN age;<\/code><\/pre>\n<h2 id=\"%e4%ba%8c%e3%80%81%e5%88%a4%e6%96%b7%e5%ad%97%e6%ae%b5%e6%98%af%e5%90%a6%e5%ad%98%e5%9c%a8-LLVVstsxpG\">\u4e8c\u3001\u5224\u65b7\u5b57\u6bb5\u662f\u5426\u5b58\u5728<\/h2>\n<p>\u5728\u522a\u9664\u5b57\u6bb5\u4e4b\u524d\uff0c\u9996\u5148\u9700\u8981\u78ba\u8a8d\u8a72\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u65bc\u8cc7\u6599\u8868\u4e2d\u3002\u4e0d\u540c\u7684\u8cc7\u6599\u5eab\u7ba1\u7406\u7cfb\u7d71\uff08DBMS\uff09\u63d0\u4f9b\u4e86\u4e0d\u540c\u7684\u65b9\u6cd5\u4f86\u6aa2\u67e5\u5b57\u6bb5\u7684\u5b58\u5728\u6027\u3002\u4ee5\u4e0b\u662f\u5e7e\u7a2e\u5e38\u898b\u7684\u8cc7\u6599\u5eab\u7cfb\u7d71\u53ca\u5176\u6aa2\u67e5\u5b57\u6bb5\u5b58\u5728\u6027\u7684\u65b9\u6cd5\uff1a<\/p>\n<h3 id=\"1-mysql-LLVVstsxpG\">1. MySQL<\/h3>\n<p>\u5728 MySQL \u4e2d\uff0c\u53ef\u4ee5\u67e5\u8a62 <code>information_schema<\/code> \u8cc7\u6599\u5eab\u4f86\u6aa2\u67e5\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u3002\u4ee5\u4e0b\u662f\u4e00\u500b\u793a\u4f8b\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT COUNT(*) \nFROM information_schema.COLUMNS \nWHERE TABLE_NAME = 'employees' \nAND COLUMN_NAME = 'age';<\/code><\/pre>\n<p>\u5982\u679c\u8fd4\u56de\u7684\u8a08\u6578\u5927\u65bc 0\uff0c\u5247\u8868\u793a\u8a72\u5b57\u6bb5\u5b58\u5728\u3002<\/p>\n<h3 id=\"2-sql-server-LLVVstsxpG\">2. SQL Server<\/h3>\n<p>\u5728 SQL Server \u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528 <code>COL_LENGTH<\/code> \u51fd\u6578\u4f86\u6aa2\u67e5\u5b57\u6bb5\u662f\u5426\u5b58\u5728\uff1a<\/p>\n<pre><code>IF COL_LENGTH('employees', 'age') IS NOT NULL\nBEGIN\n    PRINT '\u5b57\u6bb5\u5b58\u5728';\nEND\nELSE\nBEGIN\n    PRINT '\u5b57\u6bb5\u4e0d\u5b58\u5728';\nEND;<\/code><\/pre>\n<h3 id=\"3-postgresql-LLVVstsxpG\">3. PostgreSQL<\/h3>\n<p>\u5728 PostgreSQL \u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528 <code>pg_catalog<\/code> \u4f86\u6aa2\u67e5\u5b57\u6bb5\u7684\u5b58\u5728\u6027\uff1a<\/p>\n<pre><code>SELECT EXISTS (\n    SELECT 1 \n    FROM pg_catalog.pg_attribute \n    WHERE attrelid = 'employees'::regclass \n    AND attname = 'age'\n    AND NOT attisdropped\n);<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de\u4e00\u500b\u5e03\u6797\u503c\uff0c\u6307\u793a\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u3002<\/p>\n<h2 id=\"%e4%b8%89%e3%80%81%e5%88%aa%e9%99%a4%e5%ad%97%e6%ae%b5%e7%9a%84%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-LLVVstsxpG\">\u4e09\u3001\u522a\u9664\u5b57\u6bb5\u7684\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u5728\u522a\u9664\u5b57\u6bb5\u4e4b\u524d\uff0c\u61c9\u8003\u616e\u4ee5\u4e0b\u5e7e\u9ede\uff1a<\/p>\n<ul>\n<li>\u522a\u9664\u5b57\u6bb5\u5c07\u5c0e\u81f4\u8a72\u5b57\u6bb5\u4e2d\u7684\u6240\u6709\u6578\u64da\u6c38\u4e45\u4e1f\u5931\uff0c\u8acb\u78ba\u4fdd\u5728\u522a\u9664\u4e4b\u524d\u5099\u4efd\u91cd\u8981\u6578\u64da\u3002<\/li>\n<li>\u67d0\u4e9b\u8cc7\u6599\u5eab\u7cfb\u7d71\u53ef\u80fd\u6703\u5c0d\u522a\u9664\u5b57\u6bb5\u7684\u64cd\u4f5c\u6709\u7279\u5b9a\u7684\u9650\u5236\u6216\u8981\u6c42\uff0c\u8acb\u53c3\u8003\u76f8\u95dc\u6587\u6a94\u3002<\/li>\n<li>\u5728\u751f\u7522\u74b0\u5883\u4e2d\u9032\u884c\u6b64\u985e\u64cd\u4f5c\u6642\uff0c\u5efa\u8b70\u5728\u4f4e\u5cf0\u6642\u6bb5\u9032\u884c\uff0c\u4ee5\u6e1b\u5c11\u5c0d\u7528\u6236\u7684\u5f71\u97ff\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-LLVVstsxpG\">\u7e3d\u7d50<\/h2>\n<p>\u5728 SQL \u4e2d\uff0c\u522a\u9664\u5b57\u6bb5\u662f\u4e00\u500b\u91cd\u8981\u7684\u64cd\u4f5c\uff0c\u4f46\u5728\u57f7\u884c\u4e4b\u524d\u78ba\u8a8d\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u662f\u81f3\u95dc\u91cd\u8981\u7684\u3002\u4e0d\u540c\u7684\u8cc7\u6599\u5eab\u7cfb\u7d71\u63d0\u4f9b\u4e86\u4e0d\u540c\u7684\u65b9\u6cd5\u4f86\u6aa2\u67e5\u5b57\u6bb5\u7684\u5b58\u5728\u6027\uff0c\u958b\u767c\u8005\u61c9\u6839\u64da\u6240\u4f7f\u7528\u7684\u8cc7\u6599\u5eab\u9078\u64c7\u5408\u9069\u7684\u65b9\u6cd5\u3002\u4e86\u89e3\u9019\u4e9b\u57fa\u672c\u64cd\u4f5c\u4e0d\u50c5\u80fd\u63d0\u9ad8\u958b\u767c\u6548\u7387\uff0c\u9084\u80fd\u907f\u514d\u4e0d\u5fc5\u8981\u7684\u6578\u64da\u640d\u5931\u3002<\/p>\n<p>\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684 <a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a> \u89e3\u6c7a\u65b9\u6848\uff0cServer.HK \u63d0\u4f9b\u591a\u7a2e\u9078\u64c7\u4ee5\u6eff\u8db3\u60a8\u7684\u9700\u6c42\u3002\u6211\u5011\u7684 <a href=\"https:\/\/server.hk\">\u4f3a\u670d\u5668<\/a> \u670d\u52d9\u65e8\u5728\u70ba\u60a8\u63d0\u4f9b\u7a69\u5b9a\u548c\u5b89\u5168\u7684\u74b0\u5883\uff0c\u52a9\u60a8\u8f15\u9b06\u7ba1\u7406\u8cc7\u6599\u5eab\u548c\u61c9\u7528\u7a0b\u5f0f\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3\u5982\u4f55\u5728 SQL \u4e2d\u522a\u9664\u5b57\u6bb5\u53ca\u5224\u65b7\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u7684\u65b9\u6cd5\uff0c\u63d0\u5347\u6578\u64da\u5eab\u7ba1\u7406\u6548\u7387\uff0c\u78ba\u4fdd\u6578\u64da\u5b8c\u6574\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-143903","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143903","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=143903"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143903\/revisions"}],"predecessor-version":[{"id":143904,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143903\/revisions\/143904"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=143903"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=143903"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=143903"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}