{"id":66347,"date":"2024-10-14T16:42:17","date_gmt":"2024-10-14T08:42:17","guid":{"rendered":"https:\/\/server.hk\/cnblog\/66347\/"},"modified":"2024-10-14T16:42:17","modified_gmt":"2024-10-14T08:42:17","slug":"mssql%e4%b8%ad%e5%88%a4%e6%96%b7%e7%a9%ba%e5%80%bc%e7%9a%84%e5%af%a6%e7%8f%be%e6%96%b9%e5%bc%8f%ef%bc%88mssql%e5%88%a4%e6%96%b7%e7%a9%ba%e5%80%bc%ef%bc%89","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/66347\/","title":{"rendered":"MSSQL\u4e2d\u5224\u65b7\u7a7a\u503c\u7684\u5be6\u73fe\u65b9\u5f0f\uff08mssql\u5224\u65b7\u7a7a\u503c\uff09"},"content":{"rendered":"

MSSQL\u4e2d\u5224\u65b7\u7a7a\u503c\u7684\u5be6\u73fe\u65b9\u5f0f\uff08mssql\u5224\u65b7\u7a7a\u503c\uff09<\/h1>\n

\u5728\u4f7f\u7528Microsoft SQL Server\uff08MSSQL\uff09\u9032\u884c\u6578\u64da\u5eab\u7ba1\u7406\u6642\uff0c\u5224\u65b7\u7a7a\u503c\uff08NULL\uff09\u662f\u4e00\u500b\u5e38\u898b\u4e14\u91cd\u8981\u7684\u64cd\u4f5c\u3002\u7a7a\u503c\u5728\u6578\u64da\u5eab\u4e2d\u8868\u793a\u7f3a\u5931\u6216\u672a\u77e5\u7684\u6578\u64da\uff0c\u6b63\u78ba\u5730\u8655\u7406\u7a7a\u503c\u5c0d\u65bc\u6578\u64da\u7684\u5b8c\u6574\u6027\u548c\u67e5\u8a62\u7684\u6e96\u78ba\u6027\u81f3\u95dc\u91cd\u8981\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u5728MSSQL\u4e2d\u5224\u65b7\u7a7a\u503c\u7684\u5e7e\u7a2e\u5be6\u73fe\u65b9\u5f0f\uff0c\u4e26\u63d0\u4f9b\u76f8\u61c9\u7684\u793a\u4f8b\u548c\u4ee3\u78bc\u7247\u6bb5\u3002<\/p>\n

1. NULL\u7684\u57fa\u672c\u6982\u5ff5<\/h2>\n

\u5728MSSQL\u4e2d\uff0cNULL\u662f\u4e00\u500b\u7279\u6b8a\u7684\u6a19\u8a18\uff0c\u7528\u65bc\u8868\u793a\u6578\u64da\u7684\u7f3a\u5931\u3002NULL\u4e26\u4e0d\u7b49\u540c\u65bc\u96f6\u6216\u7a7a\u5b57\u7b26\u4e32\uff0c\u5b83\u8868\u793a\u4e00\u500b\u672a\u77e5\u7684\u503c\u3002\u9019\u610f\u5473\u8457\u5728\u9032\u884c\u6bd4\u8f03\u6642\uff0cNULL\u7684\u884c\u70ba\u8207\u5176\u4ed6\u6578\u64da\u985e\u578b\u6709\u6240\u4e0d\u540c\u3002<\/p>\n

2. \u4f7f\u7528IS NULL\u548cIS NOT NULL<\/h2>\n

\u6700\u5e38\u898b\u7684\u5224\u65b7\u7a7a\u503c\u7684\u65b9\u6cd5\u662f\u4f7f\u7528IS NULL\u548cIS NOT NULL\u8a9e\u53e5\u3002\u9019\u4e9b\u8a9e\u53e5\u53ef\u4ee5\u7528\u65bcWHERE\u5b50\u53e5\u4e2d\uff0c\u4ee5\u904e\u6ffe\u51fa\u5305\u542b\u6216\u4e0d\u5305\u542bNULL\u7684\u8a18\u9304\u3002<\/p>\n

SELECT * FROM Employees WHERE ManagerID IS NULL;<\/code><\/pre>\n
\u4e0a\u8ff0\u67e5\u8a62\u5c07\u8fd4\u56de\u6240\u6709\u6c92\u6709\u7d93\u7406\u7684\u54e1\u5de5\u8a18\u9304\u3002\u76f8\u5c0d\u5730\uff0c\u4f7f\u7528IS NOT NULL\u53ef\u4ee5\u67e5\u8a62\u6240\u6709\u6709\u7d93\u7406\u7684\u54e1\u5de5\uff1a<\/p>\n
SELECT * FROM Employees WHERE ManagerID IS NOT NULL;<\/code><\/pre>\n
3. \u4f7f\u7528COALESCE\u51fd\u6578<\/h2>\n
COALESCE\u51fd\u6578\u662f\u4e00\u500b\u975e\u5e38\u6709\u7528\u7684\u5de5\u5177\uff0c\u53ef\u4ee5\u7528\u4f86\u8655\u7406NULL\u503c\u3002\u5b83\u63a5\u53d7\u591a\u500b\u53c3\u6578\uff0c\u4e26\u8fd4\u56de\u7b2c\u4e00\u500b\u975eNULL\u7684\u503c\u3002\u9019\u5728\u9700\u8981\u63d0\u4f9b\u9ed8\u8a8d\u503c\u6642\u7279\u5225\u6709\u7528\u3002<\/p>\n
SELECT COALESCE(PhoneNumber, '\u7121\u96fb\u8a71') AS ContactNumber FROM Employees;<\/code><\/pre>\n
\u5728\u9019\u500b\u4f8b\u5b50\u4e2d\uff0c\u5982\u679cPhoneNumber\u70baNULL\uff0c\u5247\u8fd4\u56de’\u7121\u96fb\u8a71’\u4f5c\u70ba\u9ed8\u8a8d\u503c\u3002<\/p>\n
4. \u4f7f\u7528CASE\u8a9e\u53e5<\/h2>\n
CASE\u8a9e\u53e5\u4e5f\u53ef\u4ee5\u7528\u4f86\u5224\u65b7NULL\u503c\uff0c\u4e26\u6839\u64da\u689d\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u7d50\u679c\u3002\u9019\u5728\u9700\u8981\u9032\u884c\u66f4\u8907\u96dc\u7684\u908f\u8f2f\u5224\u65b7\u6642\u975e\u5e38\u6709\u7528\u3002<\/p>\n
SELECT \n    EmployeeName, \n    CASE \n        WHEN PhoneNumber IS NULL THEN '\u7121\u96fb\u8a71' \n        ELSE PhoneNumber \n    END AS ContactNumber \nFROM Employees;<\/code><\/pre>\n
\u9019\u6bb5\u4ee3\u78bc\u5c07\u6839\u64daPhoneNumber\u662f\u5426\u70baNULL\u4f86\u8fd4\u56de\u4e0d\u540c\u7684\u7d50\u679c\u3002<\/p>\n
5. \u4f7f\u7528NULLIF\u51fd\u6578<\/h2>\n
NULLIF\u51fd\u6578\u53ef\u4ee5\u7528\u4f86\u6bd4\u8f03\u5169\u500b\u8868\u9054\u5f0f\uff0c\u5982\u679c\u5b83\u5011\u76f8\u7b49\uff0c\u5247\u8fd4\u56deNULL\uff0c\u5426\u5247\u8fd4\u56de\u7b2c\u4e00\u500b\u8868\u9054\u5f0f\u3002\u9019\u5728\u9700\u8981\u907f\u514d\u7279\u5b9a\u503c\u6642\u975e\u5e38\u6709\u7528\u3002<\/p>\n
SELECT NULLIF(PhoneNumber, '') AS ContactNumber FROM Employees;<\/code><\/pre>\n
\u5728\u9019\u500b\u4f8b\u5b50\u4e2d\uff0c\u5982\u679cPhoneNumber\u70ba\u7a7a\u5b57\u7b26\u4e32\uff0c\u5247\u8fd4\u56deNULL\u3002<\/p>\n
6. \u5c0f\u7d50<\/h2>\n
\u5728MSSQL\u4e2d\uff0c\u6b63\u78ba\u5730\u5224\u65b7\u548c\u8655\u7406\u7a7a\u503c\u662f\u6578\u64da\u5eab\u64cd\u4f5c\u4e2d\u7684\u4e00\u500b\u91cd\u8981\u65b9\u9762\u3002\u901a\u904e\u4f7f\u7528IS NULL\u3001COALESCE\u3001CASE\u548cNULLIF\u7b49\u51fd\u6578\uff0c\u958b\u767c\u8005\u53ef\u4ee5\u9748\u6d3b\u5730\u8655\u7406\u7f3a\u5931\u7684\u6578\u64da\uff0c\u5f9e\u800c\u63d0\u9ad8\u67e5\u8a62\u7684\u6e96\u78ba\u6027\u548c\u6578\u64da\u7684\u5b8c\u6574\u6027\u3002<\/p>\n
\u5c0d\u65bc\u9700\u8981\u9ad8\u6548\u6578\u64da\u8655\u7406\u7684\u7528\u6236\uff0c\u9078\u64c7\u5408\u9069\u7684\u6578\u64da\u5eab\u89e3\u6c7a\u65b9\u6848\u81f3\u95dc\u91cd\u8981\u3002\u82e5\u60a8\u5c0d\u65bcVPS\u6216\u5176\u4ed6\u4f3a\u670d\u5668\u89e3\u6c7a\u65b9\u6848\u611f\u8208\u8da3\uff0c\u8acb\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4e86\u89e3\u66f4\u591a\u4fe1\u606f\u3002\u60a8\u53ef\u4ee5\u67e5\u770b\u6211\u5011\u7684\u9999\u6e2fVPS<\/a>\u670d\u52d9\uff0c\u7372\u53d6\u66f4\u591a\u6709\u95dc\u6578\u64da\u5eab\u7ba1\u7406\u7684\u8cc7\u6e90\u548c\u652f\u6301\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u63a2\u7d22MSSQL\u4e2d\u5224\u65b7\u7a7a\u503c\u7684\u5be6\u73fe\u65b9\u5f0f\uff0c\u4e86\u89e3\u5982\u4f55\u4f7f\u7528IS NULL\u548cCOALESCE\u7b49\u51fd\u6578\u6709\u6548\u8655\u7406\u7a7a\u503c\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-66347","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/66347","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=66347"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/66347\/revisions"}],"predecessor-version":[{"id":66348,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/66347\/revisions\/66348"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=66347"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=66347"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=66347"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}