{"id":190624,"date":"2024-11-12T14:08:28","date_gmt":"2024-11-12T06:08:28","guid":{"rendered":"https:\/\/server.hk\/cnblog\/190624\/"},"modified":"2024-11-12T14:08:29","modified_gmt":"2024-11-12T06:08:29","slug":"%e6%88%91%e5%80%91%e4%b8%80%e8%b5%b7%e8%81%8a%e8%81%8a%e5%a5%87%e6%80%aa%e7%9a%84sql%e5%95%8f%e9%a1%8c1","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/190624\/","title":{"rendered":"\u6211\u5011\u4e00\u8d77\u804a\u804a\u5947\u602a\u7684SQL\u554f\u984c+1"},"content":{"rendered":"

\u6211\u5011\u4e00\u8d77\u804a\u804a\u5947\u602a\u7684SQL\u554f\u984c+1<\/h1>\n

\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0cSQL\uff08\u7d50\u69cb\u5316\u67e5\u8a62\u8a9e\u8a00\uff09\u662f\u6700\u5e38\u7528\u7684\u8a9e\u8a00\u4e4b\u4e00\u3002\u96d6\u7136SQL\u7684\u57fa\u672c\u8a9e\u6cd5\u76f8\u5c0d\u7c21\u55ae\uff0c\u4f46\u5728\u5be6\u969b\u61c9\u7528\u4e2d\uff0c\u958b\u767c\u8005\u7d93\u5e38\u6703\u9047\u5230\u4e00\u4e9b\u5947\u602a\u7684\u554f\u984c\u3002\u9019\u4e9b\u554f\u984c\u4e0d\u50c5\u6311\u6230\u4e86\u958b\u767c\u8005\u7684\u6280\u8853\u80fd\u529b\uff0c\u4e5f\u8b93\u4eba\u5c0dSQL\u7684\u904b\u4f5c\u539f\u7406\u7522\u751f\u4e86\u66f4\u6df1\u7684\u601d\u8003\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u4e00\u4e9b\u5e38\u898b\u7684\u5947\u602aSQL\u554f\u984c\uff0c\u4e26\u63d0\u4f9b\u89e3\u6c7a\u65b9\u6848\u548c\u793a\u4f8b\u3002<\/p>\n

1. NULL\u503c\u7684\u8655\u7406<\/h2>\n

\u5728SQL\u4e2d\uff0cNULL\u503c\u4ee3\u8868\u7f3a\u5931\u6216\u672a\u77e5\u7684\u6578\u64da\u3002\u9019\u4f7f\u5f97\u5728\u9032\u884c\u67e5\u8a62\u6642\uff0cNULL\u503c\u7684\u8655\u7406\u6210\u70ba\u4e00\u500b\u5e38\u898b\u7684\u554f\u984c\u3002\u4f8b\u5982\uff0c\u7576\u6211\u5011\u4f7f\u7528\u6bd4\u8f03\u904b\u7b97\u7b26\u6642\uff0cNULL\u503c\u7684\u884c\u70ba\u53ef\u80fd\u6703\u8b93\u4eba\u56f0\u60d1\u3002<\/p>\n

SELECT * FROM users WHERE age = NULL;<\/code><\/pre>\n
\u4e0a\u8ff0\u67e5\u8a62\u4e0d\u6703\u8fd4\u56de\u4efb\u4f55\u7d50\u679c\uff0c\u56e0\u70baNULL\u4e0d\u7b49\u65bc\u4efb\u4f55\u503c\uff0c\u5305\u62ec\u5b83\u81ea\u5df1\u3002\u6b63\u78ba\u7684\u505a\u6cd5\u662f\u4f7f\u7528IS NULL\u4f86\u6aa2\u67e5NULL\u503c\uff1a<\/p>\n
SELECT * FROM users WHERE age IS NULL;<\/code><\/pre>\n
2. \u96b1\u5f0f\u985e\u578b\u8f49\u63db<\/h2>\n
SQL\u5728\u8655\u7406\u4e0d\u540c\u6578\u64da\u985e\u578b\u6642\uff0c\u6703\u81ea\u52d5\u9032\u884c\u985e\u578b\u8f49\u63db\uff0c\u9019\u6709\u6642\u6703\u5c0e\u81f4\u610f\u60f3\u4e0d\u5230\u7684\u7d50\u679c\u3002\u4f8b\u5982\uff0c\u7576\u5c07\u5b57\u7b26\u4e32\u8207\u6578\u5b57\u9032\u884c\u6bd4\u8f03\u6642\uff0cSQL\u6703\u5617\u8a66\u5c07\u5b57\u7b26\u4e32\u8f49\u63db\u70ba\u6578\u5b57\uff0c\u9019\u53ef\u80fd\u6703\u5c0e\u81f4\u932f\u8aa4\u7684\u67e5\u8a62\u7d50\u679c\u3002<\/p>\n
SELECT * FROM orders WHERE order_id = '123';<\/code><\/pre>\n
\u5982\u679corder_id\u662f\u6574\u6578\u985e\u578b\uff0c\u9019\u500b\u67e5\u8a62\u53ef\u80fd\u6703\u6b63\u5e38\u5de5\u4f5c\uff0c\u4f46\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u9019\u6a23\u7684\u96b1\u5f0f\u8f49\u63db\u53ef\u80fd\u6703\u5c0e\u81f4\u6027\u80fd\u554f\u984c\u6216\u932f\u8aa4\u7684\u7d50\u679c\u3002\u70ba\u4e86\u907f\u514d\u9019\u7a2e\u60c5\u6cc1\uff0c\u5efa\u8b70\u660e\u78ba\u6307\u5b9a\u6578\u64da\u985e\u578b\uff1a<\/p>\n
SELECT * FROM orders WHERE order_id = CAST('123' AS INT);<\/code><\/pre>\n
3. \u4f7f\u7528GROUP BY\u6642\u7684\u5947\u602a\u884c\u70ba<\/h2>\n
\u5728\u4f7f\u7528GROUP BY\u9032\u884c\u805a\u5408\u67e5\u8a62\u6642\uff0c\u958b\u767c\u8005\u7d93\u5e38\u6703\u9047\u5230\u4e00\u4e9b\u610f\u5916\u7684\u884c\u70ba\u3002\u4f8b\u5982\uff0c\u7576\u6211\u5011\u5728SELECT\u8a9e\u53e5\u4e2d\u4f7f\u7528\u672a\u805a\u5408\u7684\u5217\u6642\uff0c\u53ef\u80fd\u6703\u5c0e\u81f4\u932f\u8aa4\u6216\u4e0d\u6b63\u78ba\u7684\u7d50\u679c\u3002<\/p>\n
SELECT name, COUNT(*) FROM employees GROUP BY department;<\/code><\/pre>\n
\u9019\u6a23\u7684\u67e5\u8a62\u6703\u5c0e\u81f4\u932f\u8aa4\uff0c\u56e0\u70baname\u5217\u6c92\u6709\u88ab\u805a\u5408\u6216\u5206\u7d44\u3002\u6b63\u78ba\u7684\u505a\u6cd5\u662f\u78ba\u4fdd\u6240\u6709\u9078\u64c7\u7684\u5217\u90fd\u5728GROUP BY\u5b50\u53e5\u4e2d\uff1a<\/p>\n
SELECT department, COUNT(*) FROM employees GROUP BY department;<\/code><\/pre>\n
4. JOIN\u64cd\u4f5c\u4e2d\u7684\u610f\u5916\u7d50\u679c<\/h2>\n
\u5728\u9032\u884cJOIN\u64cd\u4f5c\u6642\uff0c\u958b\u767c\u8005\u53ef\u80fd\u6703\u9047\u5230\u610f\u5916\u7684\u7d50\u679c\uff0c\u7279\u5225\u662f\u5728\u4f7f\u7528LEFT JOIN\u6216RIGHT JOIN\u6642\u3002\u9019\u4e9bJOIN\u64cd\u4f5c\u6703\u8fd4\u56de\u6240\u6709\u4f86\u81ea\u4e00\u500b\u8868\u7684\u884c\uff0c\u5373\u4f7f\u5728\u53e6\u4e00\u500b\u8868\u4e2d\u6c92\u6709\u5339\u914d\u7684\u884c\u3002<\/p>\n
SELECT a.*, b.* FROM table_a a LEFT JOIN table_b b ON a.id = b.a_id;<\/code><\/pre>\n
\u5982\u679ctable_b\u4e2d\u6c92\u6709\u8207table_a\u5339\u914d\u7684\u884c\uff0c\u5247b\u7684\u6240\u6709\u5217\u5c07\u8fd4\u56deNULL\u3002\u9019\u53ef\u80fd\u6703\u5c0e\u81f4\u5f8c\u7e8c\u7684\u6578\u64da\u8655\u7406\u51fa\u73fe\u554f\u984c\u3002\u56e0\u6b64\uff0c\u5728\u9032\u884cJOIN\u64cd\u4f5c\u6642\uff0c\u958b\u767c\u8005\u61c9\u8a72\u4ed4\u7d30\u6aa2\u67e5\u7d50\u679c\uff0c\u4e26\u8003\u616e\u4f7f\u7528WHERE\u5b50\u53e5\u4f86\u904e\u6ffe\u4e0d\u9700\u8981\u7684NULL\u503c\u3002<\/p>\n
\u7e3d\u7d50<\/h2>\n
\u5728SQL\u7684\u4f7f\u7528\u904e\u7a0b\u4e2d\uff0c\u958b\u767c\u8005\u7d93\u5e38\u6703\u9047\u5230\u5404\u7a2e\u5947\u602a\u7684\u554f\u984c\uff0c\u9019\u4e9b\u554f\u984c\u4e0d\u50c5\u8003\u9a57\u4e86\u4ed6\u5011\u7684\u6280\u8853\u80fd\u529b\uff0c\u4e5f\u4fc3\u4f7f\u4ed6\u5011\u6df1\u5165\u7406\u89e3SQL\u7684\u904b\u4f5c\u539f\u7406\u3002\u901a\u904e\u6b63\u78ba\u8655\u7406NULL\u503c\u3001\u907f\u514d\u96b1\u5f0f\u985e\u578b\u8f49\u63db\u3001\u6b63\u78ba\u4f7f\u7528GROUP BY\u4ee5\u53ca\u8b39\u614e\u9032\u884cJOIN\u64cd\u4f5c\uff0c\u958b\u767c\u8005\u53ef\u4ee5\u6709\u6548\u5730\u89e3\u6c7a\u9019\u4e9b\u554f\u984c\u3002<\/p>\n
\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684 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 \u9999\u6e2fVPS<\/a> \u9084\u662f\u5176\u4ed6\u985e\u578b\u7684 \u4f3a\u670d\u5668<\/a>\uff0c\u6211\u5011\u90fd\u80fd\u70ba\u60a8\u63d0\u4f9b\u7a69\u5b9a\u7684\u670d\u52d9\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u63a2\u7d22\u5947\u602a\u7684SQL\u554f\u984c\uff0c\u5206\u4eab\u89e3\u6c7a\u65b9\u6848\u8207\u6280\u5de7\uff0c\u8b93\u6211\u5011\u4e00\u8d77\u6df1\u5165\u6578\u64da\u5eab\u7684\u5967\u79d8\uff0c\u63d0\u5347\u4f60\u7684SQL\u6280\u80fd\uff01<\/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-190624","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/190624","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=190624"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/190624\/revisions"}],"predecessor-version":[{"id":190625,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/190624\/revisions\/190625"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=190624"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=190624"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=190624"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}