{"id":187736,"date":"2024-11-11T16:45:20","date_gmt":"2024-11-11T08:45:20","guid":{"rendered":"https:\/\/server.hk\/cnblog\/187736\/"},"modified":"2024-11-11T16:45:22","modified_gmt":"2024-11-11T08:45:22","slug":"%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e7%9a%84%e7%a9%ba%e5%80%bc%e5%92%8c%e7%b4%a2%e5%bc%95%e5%a6%82%e4%bd%95%e5%bd%b1%e9%9f%bf%e6%95%b8%e6%93%9a%e6%9f%a5%e8%a9%a2%ef%bc%9f-%e6%95%b8%e6%93%9a%e5%ba%ab","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/187736\/","title":{"rendered":"\u6578\u64da\u5eab\u4e2d\u7684\u7a7a\u503c\u548c\u7d22\u5f15\u5982\u4f55\u5f71\u97ff\u6578\u64da\u67e5\u8a62\uff1f (\u6578\u64da\u5eab \u7a7a\u503c \u7d22\u5f15)"},"content":{"rendered":"

\u6578\u64da\u5eab\u4e2d\u7684\u7a7a\u503c\u548c\u7d22\u5f15\u5982\u4f55\u5f71\u97ff\u6578\u64da\u67e5\u8a62\uff1f<\/h1>\n

\u5728\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0c\u7a7a\u503c\uff08NULL\uff09\u548c\u7d22\u5f15\u662f\u5169\u500b\u91cd\u8981\u7684\u6982\u5ff5\uff0c\u5b83\u5011\u5c0d\u6578\u64da\u67e5\u8a62\u7684\u6027\u80fd\u548c\u7d50\u679c\u6709\u8457\u6df1\u9060\u7684\u5f71\u97ff\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u7a7a\u503c\u7684\u5b9a\u7fa9\u3001\u7d22\u5f15\u7684\u4f5c\u7528\uff0c\u4ee5\u53ca\u5b83\u5011\u5982\u4f55\u5f71\u97ff\u6578\u64da\u67e5\u8a62\u7684\u6548\u7387\u548c\u6e96\u78ba\u6027\u3002<\/p>\n

\u7a7a\u503c\u7684\u5b9a\u7fa9\u53ca\u5176\u5f71\u97ff<\/h2>\n

\u7a7a\u503c\uff08NULL\uff09\u5728\u6578\u64da\u5eab\u4e2d\u8868\u793a\u7f3a\u5931\u6216\u672a\u77e5\u7684\u6578\u64da\u3002\u5b83\u4e0d\u540c\u65bc\u96f6\u6216\u7a7a\u5b57\u7b26\u4e32\uff0c\u56e0\u70ba\u9019\u4e9b\u503c\u662f\u5177\u9ad4\u7684\uff0c\u800c\u7a7a\u503c\u5247\u8868\u793a\u201c\u7121\u503c\u201d\u3002\u5728\u6578\u64da\u5eab\u4e2d\uff0c\u7a7a\u503c\u7684\u5b58\u5728\u53ef\u80fd\u6703\u5f71\u97ff\u67e5\u8a62\u7684\u7d50\u679c\u548c\u6027\u80fd\u3002<\/p>\n

\u7a7a\u503c\u7684\u67e5\u8a62\u884c\u70ba<\/h3>\n

\u5728 SQL \u67e5\u8a62\u4e2d\uff0c\u8655\u7406\u7a7a\u503c\u9700\u8981\u7279\u5225\u6ce8\u610f\u3002\u4f7f\u7528\u5e38\u898f\u7684\u6bd4\u8f03\u904b\u7b97\u7b26\uff08\u5982 = \u6216 \uff09\u6642\uff0c\u7a7a\u503c\u7684\u884c\u70ba\u53ef\u80fd\u6703\u5c0e\u81f4\u610f\u5916\u7684\u7d50\u679c\u3002\u4f8b\u5982\uff0c\u4ee5\u4e0b\u67e5\u8a62\u5c07\u4e0d\u6703\u8fd4\u56de\u4efb\u4f55\u884c\uff1a<\/p>\n

SELECT * FROM users WHERE age = NULL;<\/code><\/pre>\n
\u6b63\u78ba\u7684\u505a\u6cd5\u662f\u4f7f\u7528 IS NULL \u6216 IS NOT NULL \u4f86\u6aa2\u67e5\u7a7a\u503c\uff1a<\/p>\n
SELECT * FROM users WHERE age IS NULL;<\/code><\/pre>\n
\u9019\u7a2e\u67e5\u8a62\u65b9\u5f0f\u80fd\u5920\u6b63\u78ba\u5730\u7be9\u9078\u51fa\u6240\u6709\u5e74\u9f61\u70ba\u7a7a\u7684\u7528\u6236\u3002<\/p>\n
\u7a7a\u503c\u5c0d\u7d22\u5f15\u7684\u5f71\u97ff<\/h3>\n
\u7a7a\u503c\u7684\u5b58\u5728\u4e5f\u6703\u5f71\u97ff\u7d22\u5f15\u7684\u6027\u80fd\u3002\u5927\u591a\u6578\u6578\u64da\u5eab\u7cfb\u7d71\u5728\u5275\u5efa\u7d22\u5f15\u6642\uff0c\u6703\u5ffd\u7565\u7a7a\u503c\u3002\u9019\u610f\u5473\u8457\uff0c\u5982\u679c\u4e00\u500b\u5217\u4e2d\u6709\u5927\u91cf\u7684\u7a7a\u503c\uff0c\u5247\u8a72\u5217\u7684\u7d22\u5f15\u53ef\u80fd\u4e0d\u6703\u5982\u9810\u671f\u822c\u63d0\u9ad8\u67e5\u8a62\u6027\u80fd\u3002\u8209\u4f8b\u4f86\u8aaa\uff0c\u8003\u616e\u4ee5\u4e0b\u60c5\u6cc1\uff1a<\/p>\n
CREATE INDEX idx_age ON users(age);<\/code><\/pre>\n
\u5982\u679c age \u5217\u4e2d\u6709\u5927\u91cf\u7684\u7a7a\u503c\uff0c\u5247\u8a72\u7d22\u5f15\u53ef\u80fd\u4e0d\u6703\u986f\u8457\u63d0\u9ad8\u57fa\u65bc\u5e74\u9f61\u7684\u67e5\u8a62\u6027\u80fd\uff0c\u56e0\u70ba\u7d22\u5f15\u4e2d\u4e0d\u5305\u542b\u9019\u4e9b\u7a7a\u503c\u3002<\/p>\n
\u7d22\u5f15\u7684\u4f5c\u7528\u53ca\u5176\u985e\u578b<\/h2>\n
\u7d22\u5f15\u662f\u6578\u64da\u5eab\u4e2d\u7528\u65bc\u52a0\u901f\u67e5\u8a62\u7684\u4e00\u7a2e\u6578\u64da\u7d50\u69cb\u3002\u5b83\u5011\u985e\u4f3c\u65bc\u66f8\u7c4d\u7684\u76ee\u9304\uff0c\u53ef\u4ee5\u5e6b\u52a9\u6578\u64da\u5eab\u5feb\u901f\u5b9a\u4f4d\u5230\u6240\u9700\u7684\u6578\u64da\u3002\u7d22\u5f15\u7684\u985e\u578b\u6709\u591a\u7a2e\uff0c\u5305\u62ec B \u6a39\u7d22\u5f15\u3001\u54c8\u5e0c\u7d22\u5f15\u548c\u5168\u6587\u7d22\u5f15\u7b49\u3002<\/p>\n
B \u6a39\u7d22\u5f15<\/h3>\n
B \u6a39\u7d22\u5f15\u662f\u6700\u5e38\u898b\u7684\u7d22\u5f15\u985e\u578b\uff0c\u9069\u7528\u65bc\u7bc4\u570d\u67e5\u8a62\u548c\u6392\u5e8f\u64cd\u4f5c\u3002\u5b83\u7684\u7d50\u69cb\u4f7f\u5f97\u67e5\u8a62\u64cd\u4f5c\u7684\u6642\u9593\u8907\u96dc\u5ea6\u70ba O(log n)\uff0c\u9019\u5c0d\u65bc\u5927\u6578\u64da\u96c6\u4f86\u8aaa\u662f\u975e\u5e38\u9ad8\u6548\u7684\u3002<\/p>\n
\u54c8\u5e0c\u7d22\u5f15<\/h3>\n
\u54c8\u5e0c\u7d22\u5f15\u5247\u9069\u5408\u7528\u65bc\u7cbe\u78ba\u67e5\u8a62\uff0c\u56e0\u70ba\u5b83\u4f7f\u7528\u54c8\u5e0c\u51fd\u6578\u4f86\u5feb\u901f\u5b9a\u4f4d\u6578\u64da\u3002\u7136\u800c\uff0c\u54c8\u5e0c\u7d22\u5f15\u4e0d\u652f\u6301\u7bc4\u570d\u67e5\u8a62\uff0c\u9019\u662f\u5176\u4e3b\u8981\u9650\u5236\u4e4b\u4e00\u3002<\/p>\n
\u5168\u6587\u7d22\u5f15<\/h3>\n
\u5168\u6587\u7d22\u5f15\u4e3b\u8981\u7528\u65bc\u6587\u672c\u641c\u7d22\uff0c\u80fd\u5920\u5feb\u901f\u67e5\u627e\u5305\u542b\u7279\u5b9a\u55ae\u8a5e\u6216\u77ed\u8a9e\u7684\u8a18\u9304\u3002\u9019\u5728\u8655\u7406\u5927\u91cf\u6587\u672c\u6578\u64da\u6642\u975e\u5e38\u6709\u7528\u3002<\/p>\n
\u7a7a\u503c\u548c\u7d22\u5f15\u7684\u7d9c\u5408\u5f71\u97ff<\/h2>\n
\u5728\u8a2d\u8a08\u6578\u64da\u5eab\u6642\uff0c\u958b\u767c\u8005\u9700\u8981\u8003\u616e\u7a7a\u503c\u548c\u7d22\u5f15\u7684\u5f71\u97ff\u3002\u904e\u591a\u7684\u7a7a\u503c\u53ef\u80fd\u6703\u5c0e\u81f4\u7d22\u5f15\u6548\u7387\u964d\u4f4e\uff0c\u800c\u4e0d\u7576\u7684\u7d22\u5f15\u8a2d\u8a08\u5247\u53ef\u80fd\u4f7f\u67e5\u8a62\u6027\u80fd\u4e0b\u964d\u3002\u56e0\u6b64\uff0c\u5408\u7406\u7684\u6578\u64da\u5efa\u6a21\u548c\u7d22\u5f15\u7b56\u7565\u662f\u81f3\u95dc\u91cd\u8981\u7684\u3002<\/p>\n
\u4f8b\u5982\uff0c\u5728\u4e00\u500b\u7528\u6236\u8cc7\u6599\u8868\u4e2d\uff0c\u5982\u679c\u67d0\u4e9b\u5217\u7d93\u5e38\u51fa\u73fe\u7a7a\u503c\uff0c\u5247\u53ef\u4ee5\u8003\u616e\u5c07\u9019\u4e9b\u5217\u8a2d\u7f6e\u70ba\u53ef\u9078\uff0c\u4e26\u5728\u67e5\u8a62\u6642\u4f7f\u7528 IS NULL \u4f86\u8655\u7406\u7a7a\u503c\u3002\u540c\u6642\uff0c\u5c0d\u65bc\u7d93\u5e38\u7528\u65bc\u67e5\u8a62\u7684\u5217\uff0c\u61c9\u8a72\u5efa\u7acb\u5408\u9069\u7684\u7d22\u5f15\uff0c\u4ee5\u63d0\u9ad8\u67e5\u8a62\u6027\u80fd\u3002<\/p>\n
\u7e3d\u7d50<\/h2>\n
\u7a7a\u503c\u548c\u7d22\u5f15\u5728\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u626e\u6f14\u8457\u91cd\u8981\u89d2\u8272\u3002\u7a7a\u503c\u7684\u5b58\u5728\u53ef\u80fd\u6703\u5f71\u97ff\u67e5\u8a62\u7684\u7d50\u679c\uff0c\u800c\u7d22\u5f15\u5247\u80fd\u5920\u63d0\u9ad8\u67e5\u8a62\u7684\u6548\u7387\u3002\u4e86\u89e3\u9019\u4e9b\u6982\u5ff5\u4e26\u5408\u7406\u61c9\u7528\uff0c\u53ef\u4ee5\u5e6b\u52a9\u958b\u767c\u8005\u8a2d\u8a08\u51fa\u66f4\u9ad8\u6548\u7684\u6578\u64da\u5eab\u7cfb\u7d71\u3002\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u5eab\u7ba1\u7406\u6216\u5176\u4ed6\u76f8\u95dc\u6280\u8853\u6709\u8208\u8da3\uff0c\u6b61\u8fce\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4e86\u89e3\u66f4\u591a\u8cc7\u8a0a\uff0c\u63a2\u7d22\u6211\u5011\u7684 VPS<\/a> \u89e3\u6c7a\u65b9\u6848\uff0c\u63d0\u5347\u60a8\u7684\u6578\u64da\u8655\u7406\u80fd\u529b\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u63a2\u8a0e\u6578\u64da\u5eab\u4e2d\u7684\u7a7a\u503c\u548c\u7d22\u5f15\u5982\u4f55\u5f71\u97ff\u6578\u64da\u67e5\u8a62\u6548\u7387\uff0c\u63ed\u793a\u5176\u5c0d\u6027\u80fd\u548c\u7d50\u679c\u6e96\u78ba\u6027\u7684\u95dc\u9375\u4f5c\u7528\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-187736","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/187736","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=187736"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/187736\/revisions"}],"predecessor-version":[{"id":187737,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/187736\/revisions\/187737"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=187736"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=187736"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=187736"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}