{"id":194491,"date":"2024-11-13T07:06:18","date_gmt":"2024-11-12T23:06:18","guid":{"rendered":"https:\/\/server.hk\/cnblog\/194491\/"},"modified":"2024-11-13T07:06:19","modified_gmt":"2024-11-12T23:06:19","slug":"%e7%94%a8%ef%bc%9f-%e6%95%b8%e6%93%9a%e5%ba%ab%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%e6%80%8e%e9%ba%bc","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/194491\/","title":{"rendered":"\u7528\uff1f (\u6578\u64da\u5eab\u95dc\u4fc2\u4ee3\u6578\u600e\u9ebc)"},"content":{"rendered":"<h1 id=\"%e7%94%a8%ef%bc%9f-%e6%95%b8%e6%93%9a%e5%ba%ab%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%e6%80%8e%e9%ba%bc-HmXinmQUbL\">\u7528\uff1f (\u6578\u64da\u5eab\u95dc\u4fc2\u4ee3\u6578\u600e\u9ebc)<\/h1>\n<p>\u6578\u64da\u5eab\u95dc\u4fc2\u4ee3\u6578\u662f\u4e00\u7a2e\u7528\u65bc\u64cd\u4f5c\u95dc\u4fc2\u6578\u64da\u5eab\u7684\u6578\u5b78\u8a9e\u8a00\u3002\u5b83\u63d0\u4f9b\u4e86\u4e00\u7d44\u64cd\u4f5c\uff0c\u9019\u4e9b\u64cd\u4f5c\u53ef\u4ee5\u7528\u4f86\u67e5\u8a62\u548c\u4fee\u6539\u6578\u64da\u5eab\u4e2d\u7684\u6578\u64da\u3002\u95dc\u4fc2\u4ee3\u6578\u7684\u57fa\u672c\u6982\u5ff5\u6e90\u65bc\u96c6\u5408\u8ad6\uff0c\u4e26\u4e14\u5b83\u7684\u64cd\u4f5c\u53ef\u4ee5\u88ab\u8996\u70ba\u5c0d\u6578\u64da\u96c6\u7684\u96c6\u5408\u904b\u7b97\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0e\u6578\u64da\u5eab\u95dc\u4fc2\u4ee3\u6578\u7684\u57fa\u672c\u64cd\u4f5c\u53ca\u5176\u61c9\u7528\u3002<\/p>\n<h2 id=\"%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%e7%9a%84%e5%9f%ba%e6%9c%ac%e6%a6%82%e5%bf%b5-HmXinmQUbL\">\u95dc\u4fc2\u4ee3\u6578\u7684\u57fa\u672c\u6982\u5ff5<\/h2>\n<p>\u5728\u6578\u64da\u5eab\u4e2d\uff0c\u6578\u64da\u901a\u5e38\u4ee5\u8868\u683c\u7684\u5f62\u5f0f\u5b58\u5132\uff0c\u6bcf\u500b\u8868\u683c\u7531\u884c\u548c\u5217\u7d44\u6210\u3002\u6bcf\u4e00\u884c\u4ee3\u8868\u4e00\u500b\u8a18\u9304\uff0c\u800c\u6bcf\u4e00\u5217\u5247\u4ee3\u8868\u4e00\u500b\u5c6c\u6027\u3002\u95dc\u4fc2\u4ee3\u6578\u7684\u4e3b\u8981\u76ee\u7684\u662f\u5c0d\u9019\u4e9b\u8868\u683c\u9032\u884c\u64cd\u4f5c\uff0c\u4ee5\u4fbf\u5f9e\u4e2d\u63d0\u53d6\u6240\u9700\u7684\u4fe1\u606f\u3002<\/p>\n<h3 id=\"%e5%9f%ba%e6%9c%ac%e6%93%8d%e4%bd%9c-HmXinmQUbL\">\u57fa\u672c\u64cd\u4f5c<\/h3>\n<p>\u95dc\u4fc2\u4ee3\u6578\u5305\u542b\u5e7e\u500b\u57fa\u672c\u64cd\u4f5c\uff0c\u9019\u4e9b\u64cd\u4f5c\u53ef\u4ee5\u7d44\u5408\u4f7f\u7528\u4ee5\u9054\u5230\u66f4\u8907\u96dc\u7684\u67e5\u8a62\u9700\u6c42\u3002\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4e3b\u8981\u7684\u64cd\u4f5c\uff1a<\/p>\n<ul>\n<li><strong>\u9078\u64c7\uff08Selection\uff09<\/strong>: \u5f9e\u95dc\u4fc2\u4e2d\u9078\u64c7\u6eff\u8db3\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u3002\u9019\u500b\u64cd\u4f5c\u901a\u5e38\u7528\u7b26\u865f\u03c3\u8868\u793a\u3002<\/li>\n<li><strong>\u6295\u5f71\uff08Projection\uff09<\/strong>: \u5f9e\u95dc\u4fc2\u4e2d\u9078\u64c7\u7279\u5b9a\u7684\u5217\u3002\u9019\u500b\u64cd\u4f5c\u7528\u7b26\u865f\u03c0\u8868\u793a\u3002<\/li>\n<li><strong>\u806f\u63a5\uff08Join\uff09<\/strong>: \u5c07\u5169\u500b\u95dc\u4fc2\u6839\u64da\u5171\u540c\u7684\u5c6c\u6027\u9032\u884c\u5408\u4f75\u3002\u9019\u500b\u64cd\u4f5c\u53ef\u4ee5\u662f\u5167\u806f\u63a5\u3001\u5916\u806f\u63a5\u7b49\u3002<\/li>\n<li><strong>\u4e26\u96c6\uff08Union\uff09<\/strong>: \u5c07\u5169\u500b\u95dc\u4fc2\u7684\u6240\u6709\u884c\u5408\u4f75\uff0c\u53bb\u9664\u91cd\u8907\u7684\u884c\u3002\u9019\u500b\u64cd\u4f5c\u7528\u7b26\u865f\u222a\u8868\u793a\u3002<\/li>\n<li><strong>\u5dee\u96c6\uff08Difference\uff09<\/strong>: \u5f9e\u4e00\u500b\u95dc\u4fc2\u4e2d\u522a\u9664\u53e6\u4e00\u500b\u95dc\u4fc2\u4e2d\u7684\u884c\u3002\u9019\u500b\u64cd\u4f5c\u7528\u7b26\u865f\uff0d\u8868\u793a\u3002<\/li>\n<li><strong>\u7b1b\u5361\u723e\u7a4d\uff08Cartesian Product\uff09<\/strong>: \u5c07\u5169\u500b\u95dc\u4fc2\u7684\u6bcf\u4e00\u884c\u9032\u884c\u7d44\u5408\uff0c\u751f\u6210\u6240\u6709\u53ef\u80fd\u7684\u884c\u7d44\u5408\u3002\u9019\u500b\u64cd\u4f5c\u7528\u7b26\u865f\u00d7\u8868\u793a\u3002<\/li>\n<\/ul>\n<h3 id=\"%e6%93%8d%e4%bd%9c%e7%a4%ba%e4%be%8b-HmXinmQUbL\">\u64cd\u4f5c\u793a\u4f8b<\/h3>\n<p>\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4f7f\u7528\u95dc\u4fc2\u4ee3\u6578\u9032\u884c\u67e5\u8a62\u7684\u793a\u4f8b\uff1a<\/p>\n<pre><code>\n-- \u5047\u8a2d\u6709\u4e00\u500b\u5b78\u751f\u8868\u683c Students \u548c\u4e00\u500b\u8ab2\u7a0b\u8868\u683c Courses\n-- \u9078\u64c7\u6240\u6709\u5e74\u9f61\u5927\u65bc20\u7684\u5b78\u751f\n\u03c3(age &gt; 20)(Students)\n\n-- \u6295\u5f71\u51fa\u6240\u6709\u5b78\u751f\u7684\u59d3\u540d\u548c\u5e74\u9f61\n\u03c0(name, age)(Students)\n\n-- \u5167\u806f\u63a5\u5b78\u751f\u548c\u8ab2\u7a0b\u8868\u683c\uff0c\u6839\u64da\u5b78\u751fID\nStudents \u2a1d Courses ON Students.student_id = Courses.student_id\n\n-- \u7372\u53d6\u6240\u6709\u9078\u4fee\u8ab2\u7a0b\u7684\u5b78\u751f\n\u03c0(name)(\u03c3(course = 'Math')(Courses))\n<\/code><\/pre>\n<h2 id=\"%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%e7%9a%84%e6%87%89%e7%94%a8-HmXinmQUbL\">\u95dc\u4fc2\u4ee3\u6578\u7684\u61c9\u7528<\/h2>\n<p>\u95dc\u4fc2\u4ee3\u6578\u5728\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u626e\u6f14\u8457\u91cd\u8981\u89d2\u8272\u3002\u5b83\u4e0d\u50c5\u662fSQL\u8a9e\u8a00\u7684\u7406\u8ad6\u57fa\u790e\uff0c\u9084\u5e6b\u52a9\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\uff08DBMS\uff09\u512a\u5316\u67e5\u8a62\u3002\u901a\u904e\u5c07\u8907\u96dc\u7684\u67e5\u8a62\u8f49\u63db\u70ba\u57fa\u672c\u7684\u95dc\u4fc2\u4ee3\u6578\u64cd\u4f5c\uff0cDBMS\u53ef\u4ee5\u66f4\u6709\u6548\u5730\u57f7\u884c\u67e5\u8a62\uff0c\u5f9e\u800c\u63d0\u9ad8\u6027\u80fd\u3002<\/p>\n<p>\u6b64\u5916\uff0c\u95dc\u4fc2\u4ee3\u6578\u9084\u53ef\u4ee5\u7528\u65bc\u6578\u64da\u5eab\u8a2d\u8a08\u548c\u6578\u64da\u5b8c\u6574\u6027\u6aa2\u67e5\u3002\u8a2d\u8a08\u826f\u597d\u7684\u6578\u64da\u5eab\u7d50\u69cb\u53ef\u4ee5\u78ba\u4fdd\u6578\u64da\u7684\u4e00\u81f4\u6027\u548c\u6e96\u78ba\u6027\uff0c\u800c\u95dc\u4fc2\u4ee3\u6578\u63d0\u4f9b\u7684\u64cd\u4f5c\u5247\u53ef\u4ee5\u5e6b\u52a9\u6aa2\u67e5\u9019\u4e9b\u689d\u4ef6\u662f\u5426\u5f97\u5230\u6eff\u8db3\u3002<\/p>\n<h2 id=\"%e7%b8%bd%e7%b5%90-HmXinmQUbL\">\u7e3d\u7d50<\/h2>\n<p>\u6578\u64da\u5eab\u95dc\u4fc2\u4ee3\u6578\u662f\u4e00\u7a2e\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u7528\u6236\u6709\u6548\u5730\u67e5\u8a62\u548c\u64cd\u4f5c\u6578\u64da\u3002\u901a\u904e\u7406\u89e3\u5176\u57fa\u672c\u64cd\u4f5c\uff0c\u958b\u767c\u8005\u53ef\u4ee5\u66f4\u597d\u5730\u8a2d\u8a08\u548c\u512a\u5316\u6578\u64da\u5eab\u67e5\u8a62\u3002\u5c0d\u65bc\u9700\u8981\u9ad8\u6548\u6578\u64da\u8655\u7406\u7684\u61c9\u7528\uff0c\u9078\u64c7\u5408\u9069\u7684\u6578\u64da\u5eab\u89e3\u6c7a\u65b9\u6848\u81f3\u95dc\u91cd\u8981\u3002\u82e5\u60a8\u5c0d\u65bc <a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a> \u6216\u5176\u4ed6 <a href=\"https:\/\/server.hk\">\u4f3a\u670d\u5668<\/a> \u89e3\u6c7a\u65b9\u6848\u611f\u8208\u8da3\uff0c\u8acb\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4ee5\u7372\u53d6\u66f4\u591a\u4fe1\u606f\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u63a2\u7d22\u6578\u64da\u5eab\u95dc\u4fc2\u4ee3\u6578\u7684\u57fa\u672c\u6982\u5ff5\u8207\u64cd\u4f5c\uff0c\u5b78\u7fd2\u5982\u4f55\u6709\u6548\u5730\u67e5\u8a62\u548c\u7ba1\u7406\u6578\u64da\uff0c\u63d0\u5347\u6578\u64da\u8655\u7406\u80fd\u529b\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-194491","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/194491","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=194491"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/194491\/revisions"}],"predecessor-version":[{"id":194492,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/194491\/revisions\/194492"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=194491"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=194491"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=194491"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}