{"id":138459,"date":"2024-10-31T14:39:18","date_gmt":"2024-10-31T06:39:18","guid":{"rendered":"https:\/\/server.hk\/cnblog\/138459\/"},"modified":"2024-10-31T14:39:19","modified_gmt":"2024-10-31T06:39:19","slug":"sql-server%e8%99%95%e7%90%86%e7%a9%ba%e5%80%bc%e6%93%8d%e4%bd%9c%e4%b8%ad%e7%9a%843%e5%a4%a7%e5%95%8f%e9%a1%8c%e6%9c%89%e5%93%aa%e4%ba%9b%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/138459\/","title":{"rendered":"SQL Server\u8655\u7406\u7a7a\u503c\u64cd\u4f5c\u4e2d\u76843\u5927\u554f\u984c\u6709\u54ea\u4e9b\uff1f"},"content":{"rendered":"

SQL Server\u8655\u7406\u7a7a\u503c\u64cd\u4f5c\u4e2d\u76843\u5927\u554f\u984c<\/h1>\n

\u5728\u8cc7\u6599\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0c\u7a7a\u503c\uff08NULL\uff09\u662f\u4e00\u500b\u91cd\u8981\u7684\u6982\u5ff5\uff0c\u5c24\u5176\u662f\u5728SQL Server\u4e2d\u3002\u7a7a\u503c\u4ee3\u8868\u8457\u7f3a\u5931\u7684\u8cc7\u6599\u6216\u672a\u77e5\u7684\u503c\uff0c\u9019\u5728\u6578\u64da\u8655\u7406\u548c\u67e5\u8a62\u4e2d\u53ef\u80fd\u6703\u5f15\u767c\u4e00\u4e9b\u554f\u984c\u3002\u672c\u6587\u5c07\u63a2\u8a0eSQL Server\u5728\u8655\u7406\u7a7a\u503c\u64cd\u4f5c\u6642\u7684\u4e09\u5927\u4e3b\u8981\u554f\u984c\uff0c\u4e26\u63d0\u4f9b\u76f8\u61c9\u7684\u89e3\u6c7a\u65b9\u6848\u548c\u7bc4\u4f8b\u3002<\/p>\n

\u554f\u984c\u4e00\uff1a\u7a7a\u503c\u7684\u6bd4\u8f03<\/h2>\n

\u5728SQL Server\u4e2d\uff0c\u7a7a\u503c\u7684\u6bd4\u8f03\u884c\u70ba\u53ef\u80fd\u6703\u8b93\u8a31\u591a\u958b\u767c\u8005\u611f\u5230\u56f0\u60d1\u3002\u6839\u64daSQL\u6a19\u6e96\uff0c\u4efb\u4f55\u8207NULL\u7684\u6bd4\u8f03\u7d50\u679c\u90fd\u662fNULL\uff0c\u5305\u62ec\u8207NULL\u81ea\u8eab\u7684\u6bd4\u8f03\u3002\u9019\u610f\u5473\u8457\uff0c\u5982\u679c\u4f60\u5617\u8a66\u4f7f\u7528\u7b49\u865f\uff08=\uff09\u4f86\u6bd4\u8f03\u4e00\u500b\u7a7a\u503c\uff0c\u7d50\u679c\u5c07\u4e0d\u6703\u662fTRUE\uff0c\u800c\u662fNULL\u3002<\/p>\n

SELECT * FROM Employees WHERE ManagerID = NULL; -- \u9019\u5c07\u4e0d\u8fd4\u56de\u4efb\u4f55\u7d50\u679c<\/code><\/pre>\n
\u70ba\u4e86\u89e3\u6c7a\u9019\u500b\u554f\u984c\uff0c\u61c9\u4f7f\u7528IS NULL\u6216IS NOT NULL\u4f86\u9032\u884c\u7a7a\u503c\u7684\u6aa2\u67e5\u3002\u4f8b\u5982\uff1a<\/p>\n
SELECT * FROM Employees WHERE ManagerID IS NULL; -- \u9019\u5c07\u8fd4\u56de\u6240\u6709ManagerID\u70baNULL\u7684\u8a18\u9304<\/code><\/pre>\n
\u554f\u984c\u4e8c\uff1a\u805a\u5408\u51fd\u6578\u7684\u884c\u70ba<\/h2>\n
\u5728\u4f7f\u7528\u805a\u5408\u51fd\u6578\uff08\u5982SUM\u3001AVG\u3001COUNT\u7b49\uff09\u6642\uff0c\u7a7a\u503c\u7684\u5b58\u5728\u6703\u5f71\u97ff\u7d50\u679c\u3002\u5927\u591a\u6578\u805a\u5408\u51fd\u6578\u6703\u81ea\u52d5\u5ffd\u7565\u7a7a\u503c\uff0c\u4f46\u9019\u53ef\u80fd\u6703\u5c0e\u81f4\u610f\u5916\u7684\u7d50\u679c\u3002\u4f8b\u5982\uff0c\u7576\u8a08\u7b97\u5e73\u5747\u503c\u6642\uff0c\u7a7a\u503c\u4e0d\u6703\u88ab\u8a08\u5165\u8a08\u7b97\u4e2d\uff0c\u9019\u53ef\u80fd\u6703\u4f7f\u5f97\u7d50\u679c\u4e0d\u5982\u9810\u671f\u3002<\/p>\n
SELECT AVG(Salary) FROM Employees; -- \u5982\u679c\u6709Salary\u70baNULL\u7684\u8a18\u9304\uff0c\u9019\u5c07\u53ea\u8a08\u7b97\u975eNULL\u7684Salary<\/code><\/pre>\n
\u70ba\u4e86\u907f\u514d\u9019\u7a2e\u60c5\u6cc1\uff0c\u958b\u767c\u8005\u53ef\u4ee5\u4f7f\u7528COALESCE\u51fd\u6578\u4f86\u66ff\u63db\u7a7a\u503c\u3002\u4f8b\u5982\uff1a<\/p>\n
SELECT AVG(COALESCE(Salary, 0)) FROM Employees; -- \u5c07NULL\u66ff\u63db\u70ba0\u9032\u884c\u8a08\u7b97<\/code><\/pre>\n
\u554f\u984c\u4e09\uff1a\u7a7a\u503c\u5728JOIN\u64cd\u4f5c\u4e2d\u7684\u5f71\u97ff<\/h2>\n
\u5728\u9032\u884cJOIN\u64cd\u4f5c\u6642\uff0c\u7a7a\u503c\u53ef\u80fd\u6703\u5c0e\u81f4\u610f\u5916\u7684\u7d50\u679c\u3002\u7576\u4e00\u500b\u8868\u4e2d\u7684\u67d0\u500b\u6b04\u4f4d\u70baNULL\u6642\uff0c\u9019\u500b\u6b04\u4f4d\u5728JOIN\u6642\u4e0d\u6703\u5339\u914d\u4efb\u4f55\u503c\uff0c\u9019\u53ef\u80fd\u6703\u5c0e\u81f4\u67d0\u4e9b\u8a18\u9304\u88ab\u6392\u9664\u5728\u7d50\u679c\u4e4b\u5916\u3002<\/p>\n
SELECT e.Name, d.DepartmentName \nFROM Employees e \nLEFT JOIN Departments d ON e.DepartmentID = d.DepartmentID \nWHERE d.DepartmentID IS NULL; -- \u9019\u5c07\u8fd4\u56de\u6240\u6709\u6c92\u6709\u90e8\u9580\u7684\u54e1\u5de5<\/code><\/pre>\n
\u70ba\u4e86\u78ba\u4fddJOIN\u64cd\u4f5c\u7684\u6b63\u78ba\u6027\uff0c\u958b\u767c\u8005\u61c9\u8a72\u4ed4\u7d30\u8003\u616e\u7a7a\u503c\u7684\u5f71\u97ff\uff0c\u4e26\u6839\u64da\u9700\u8981\u4f7f\u7528OUTER JOIN\u4f86\u4fdd\u7559\u7a7a\u503c\u8a18\u9304\u3002<\/p>\n
\u7e3d\u7d50<\/h2>\n
\u5728SQL Server\u4e2d\uff0c\u7a7a\u503c\u7684\u8655\u7406\u662f\u4e00\u500b\u8907\u96dc\u4f46\u91cd\u8981\u7684\u8ab2\u984c\u3002\u958b\u767c\u8005\u9700\u8981\u4e86\u89e3\u7a7a\u503c\u7684\u6bd4\u8f03\u884c\u70ba\u3001\u805a\u5408\u51fd\u6578\u7684\u5f71\u97ff\u4ee5\u53caJOIN\u64cd\u4f5c\u4e2d\u7684\u6f5b\u5728\u554f\u984c\u3002\u901a\u904e\u4f7f\u7528\u9069\u7576\u7684SQL\u8a9e\u53e5\u548c\u51fd\u6578\uff0c\u53ef\u4ee5\u6709\u6548\u5730\u7ba1\u7406\u548c\u8655\u7406\u7a7a\u503c\uff0c\u5f9e\u800c\u63d0\u9ad8\u6578\u64da\u67e5\u8a62\u7684\u6e96\u78ba\u6027\u548c\u6548\u7387\u3002<\/p>\n
\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684 \u9999\u6e2fVPS<\/a> \u89e3\u6c7a\u65b9\u6848\uff0cServer.HK\u63d0\u4f9b\u591a\u7a2e\u9078\u64c7\uff0c\u5e6b\u52a9\u60a8\u66f4\u597d\u5730\u7ba1\u7406\u60a8\u7684\u6578\u64da\u5eab\u548c\u61c9\u7528\u7a0b\u5e8f\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u63a2\u7d22SQL Server\u4e2d\u8655\u7406\u7a7a\u503c\u7684\u4e09\u5927\u554f\u984c\uff0c\u5305\u62ec\u7a7a\u503c\u6bd4\u8f03\u3001\u805a\u5408\u51fd\u6578\u5f71\u97ff\u53ca\u67e5\u8a62\u6027\u80fd\u6311\u6230\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-138459","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/138459","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=138459"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/138459\/revisions"}],"predecessor-version":[{"id":138460,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/138459\/revisions\/138460"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=138459"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=138459"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=138459"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}