{"id":78908,"date":"2024-10-16T12:26:18","date_gmt":"2024-10-16T04:26:18","guid":{"rendered":"https:\/\/server.hk\/cnblog\/78908\/"},"modified":"2024-10-16T12:26:18","modified_gmt":"2024-10-16T04:26:18","slug":"mysql%e6%8c%87%e4%bb%a4-left-join%ef%bc%88%e5%b7%a6%e9%80%a3%e6%8e%a5%ef%bc%89","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/78908\/","title":{"rendered":"MySQL\u6307\u4ee4: LEFT JOIN\uff08\u5de6\u9023\u63a5\uff09"},"content":{"rendered":"<h1 id=\"mysql%e6%8c%87%e4%bb%a4-left-join%ef%bc%88%e5%b7%a6%e9%80%a3%e6%8e%a5%ef%bc%89-QDPBBLqcPN\">MySQL\u6307\u4ee4: LEFT JOIN\uff08\u5de6\u9023\u63a5\uff09<\/h1>\n<p>\u5728\u95dc\u806f\u5f0f\u8cc7\u6599\u5eab\u4e2d\uff0c\u8cc7\u6599\u7684\u67e5\u8a62\u548c\u6574\u5408\u662f\u975e\u5e38\u91cd\u8981\u7684\u3002MySQL\u4f5c\u70ba\u4e00\u7a2e\u6d41\u884c\u7684\u8cc7\u6599\u5eab\u7ba1\u7406\u7cfb\u7d71\uff0c\u63d0\u4f9b\u4e86\u591a\u7a2e\u67e5\u8a62\u65b9\u5f0f\uff0c\u5176\u4e2d\u4e4b\u4e00\u4fbf\u662fLEFT JOIN\uff08\u5de6\u9023\u63a5\uff09\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eLEFT JOIN\u7684\u6982\u5ff5\u3001\u8a9e\u6cd5\u53ca\u5176\u61c9\u7528\u7bc4\u4f8b\uff0c\u5e6b\u52a9\u8b80\u8005\u66f4\u597d\u5730\u7406\u89e3\u9019\u4e00\u6307\u4ee4\u7684\u4f7f\u7528\u3002<\/p>\n<h2 id=\"%e4%bb%80%e9%ba%bc%e6%98%afleft-join%ef%bc%9f-QDPBBLqcPN\">\u4ec0\u9ebc\u662fLEFT JOIN\uff1f<\/h2>\n<p>LEFT JOIN\u662f\u4e00\u7a2e\u7528\u65bc\u5f9e\u5169\u500b\u6216\u591a\u500b\u8cc7\u6599\u8868\u4e2d\u67e5\u8a62\u8cc7\u6599\u7684\u65b9\u5f0f\u3002\u5b83\u7684\u7279\u9ede\u662f\u8fd4\u56de\u5de6\u5074\u8cc7\u6599\u8868\u4e2d\u7684\u6240\u6709\u8a18\u9304\uff0c\u5373\u4f7f\u5728\u53f3\u5074\u8cc7\u6599\u8868\u4e2d\u6c92\u6709\u5339\u914d\u7684\u8a18\u9304\u3002\u9019\u610f\u5473\u8457\uff0c\u5982\u679c\u5de6\u5074\u8cc7\u6599\u8868\u4e2d\u7684\u67d0\u4e9b\u8a18\u9304\u5728\u53f3\u5074\u8cc7\u6599\u8868\u4e2d\u627e\u4e0d\u5230\u5c0d\u61c9\u7684\u8cc7\u6599\uff0c\u9019\u4e9b\u8a18\u9304\u4ecd\u7136\u6703\u88ab\u5305\u542b\u5728\u7d50\u679c\u4e2d\uff0c\u800c\u53f3\u5074\u8cc7\u6599\u8868\u7684\u76f8\u61c9\u6b04\u4f4d\u5247\u6703\u986f\u793a\u70baNULL\u3002<\/p>\n<h2 id=\"left-join%e7%9a%84%e8%aa%9e%e6%b3%95-QDPBBLqcPN\">LEFT JOIN\u7684\u8a9e\u6cd5<\/h2>\n<p>LEFT JOIN\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>SELECT \u6b04\u4f4d1, \u6b04\u4f4d2, ...\nFROM \u5de6\u5074\u8cc7\u6599\u8868\nLEFT JOIN \u53f3\u5074\u8cc7\u6599\u8868\nON \u5de6\u5074\u8cc7\u6599\u8868.\u6b04\u4f4d = \u53f3\u5074\u8cc7\u6599\u8868.\u6b04\u4f4d;<\/code><\/pre>\n<p>\u5728\u9019\u88e1\uff0c\u60a8\u9700\u8981\u66ff\u63db\u201c\u6b04\u4f4d1\u201d\u3001\u201c\u6b04\u4f4d2\u201d\u7b49\u70ba\u60a8\u5e0c\u671b\u67e5\u8a62\u7684\u5177\u9ad4\u6b04\u4f4d\u540d\u7a31\uff0c\u4e26\u6307\u5b9a\u5de6\u5074\u548c\u53f3\u5074\u8cc7\u6599\u8868\u7684\u540d\u7a31\u53ca\u5176\u95dc\u806f\u7684\u6b04\u4f4d\u3002<\/p>\n<h2 id=\"left-join%e7%9a%84%e6%87%89%e7%94%a8%e7%af%84%e4%be%8b-QDPBBLqcPN\">LEFT JOIN\u7684\u61c9\u7528\u7bc4\u4f8b<\/h2>\n<p>\u70ba\u4e86\u66f4\u597d\u5730\u7406\u89e3LEFT JOIN\u7684\u4f7f\u7528\uff0c\u4ee5\u4e0b\u662f\u4e00\u500b\u5177\u9ad4\u7684\u7bc4\u4f8b\u3002<\/p>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u5169\u500b\u8cc7\u6599\u8868\uff1a<strong>customers<\/strong>\uff08\u9867\u5ba2\uff09\u548c<strong>orders<\/strong>\uff08\u8a02\u55ae\uff09\u3002<\/p>\n<ul>\n<li><strong>customers<\/strong>\u8cc7\u6599\u8868\uff1a<\/li>\n<ul>\n<li>customer_id<\/li>\n<li>customer_name<\/li>\n<\/ul>\n<li><strong>orders<\/strong>\u8cc7\u6599\u8868\uff1a<\/li>\n<ul>\n<li>order_id<\/li>\n<li>customer_id<\/li>\n<li>order_date<\/li>\n<\/ul>\n<\/ul>\n<p>\u5982\u679c\u6211\u5011\u60f3\u8981\u67e5\u8a62\u6240\u6709\u9867\u5ba2\u53ca\u5176\u8a02\u55ae\u7684\u8cc7\u8a0a\uff0c\u5373\u4f7f\u67d0\u4e9b\u9867\u5ba2\u6c92\u6709\u4e0b\u904e\u8a02\u55ae\uff0c\u6211\u5011\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u7684LEFT JOIN\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT customers.customer_id, customers.customer_name, orders.order_id, orders.order_date\nFROM customers\nLEFT JOIN orders ON customers.customer_id = orders.customer_id;<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de\u6240\u6709\u9867\u5ba2\u7684ID\u548c\u540d\u7a31\uff0c\u4e26\u4e14\u5982\u679c\u9867\u5ba2\u6709\u8a02\u55ae\uff0c\u5247\u6703\u986f\u793a\u76f8\u61c9\u7684\u8a02\u55aeID\u548c\u8a02\u55ae\u65e5\u671f\uff1b\u5982\u679c\u9867\u5ba2\u6c92\u6709\u8a02\u55ae\uff0c\u5247\u8a02\u55aeID\u548c\u8a02\u55ae\u65e5\u671f\u5c07\u986f\u793a\u70baNULL\u3002<\/p>\n<h2 id=\"left-join%e7%9a%84%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-QDPBBLqcPN\">LEFT JOIN\u7684\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u5728\u4f7f\u7528LEFT JOIN\u6642\uff0c\u6709\u5e7e\u9ede\u9700\u8981\u6ce8\u610f\uff1a<\/p>\n<ul>\n<li>\u6027\u80fd\uff1aLEFT JOIN\u53ef\u80fd\u6703\u5f71\u97ff\u67e5\u8a62\u6027\u80fd\uff0c\u7279\u5225\u662f\u5728\u8cc7\u6599\u8868\u975e\u5e38\u5927\u7684\u60c5\u6cc1\u4e0b\u3002\u56e0\u6b64\uff0c\u61c9\u8b39\u614e\u4f7f\u7528\uff0c\u4e26\u8003\u616e\u7d22\u5f15\u7684\u8a2d\u7f6e\u3002<\/li>\n<li>NULL\u503c\uff1a\u5728\u7d50\u679c\u4e2d\u51fa\u73feNULL\u503c\u6642\uff0c\u9700\u7279\u5225\u6ce8\u610f\u9019\u4e9b\u503c\u7684\u8655\u7406\uff0c\u907f\u514d\u5728\u5f8c\u7e8c\u7684\u6578\u64da\u8655\u7406\u4e2d\u51fa\u73fe\u932f\u8aa4\u3002<\/li>\n<li>\u591a\u91cd\u9023\u63a5\uff1a\u53ef\u4ee5\u4f7f\u7528\u591a\u500bLEFT JOIN\u4f86\u9023\u63a5\u591a\u500b\u8cc7\u6599\u8868\uff0c\u4f46\u9019\u6703\u589e\u52a0\u67e5\u8a62\u7684\u8907\u96dc\u6027\u548c\u57f7\u884c\u6642\u9593\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-QDPBBLqcPN\">\u7e3d\u7d50<\/h2>\n<p>LEFT JOIN\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u958b\u767c\u8005\u5f9e\u591a\u500b\u8cc7\u6599\u8868\u4e2d\u63d0\u53d6\u6240\u9700\u7684\u8cc7\u8a0a\u3002\u900f\u904e\u6b63\u78ba\u7684\u4f7f\u7528LEFT JOIN\uff0c\u60a8\u53ef\u4ee5\u7372\u5f97\u66f4\u5168\u9762\u7684\u6578\u64da\u8996\u5716\uff0c\u5f9e\u800c\u652f\u6301\u66f4\u6df1\u5165\u7684\u5206\u6790\u548c\u6c7a\u7b56\u3002\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684\u8cc7\u6599\u5eab\u89e3\u6c7a\u65b9\u6848\uff0c\u8003\u616e\u4f7f\u7528<a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a>\u4f86\u642d\u5efa\u60a8\u7684MySQL\u74b0\u5883\uff0c\u4eab\u53d7\u66f4\u7a69\u5b9a\u7684\u6027\u80fd\u548c\u66f4\u9ad8\u7684\u5b89\u5168\u6027\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3MySQL\u4e2d\u7684LEFT JOIN\uff08\u5de6\u9023\u63a5\uff09\u6307\u4ee4\uff0c\u5b78\u7fd2\u5982\u4f55\u5f9e\u5169\u500b\u8868\u4e2d\u63d0\u53d6\u76f8\u95dc\u6578\u64da\uff0c\u4fdd\u7559\u5de6\u5074\u8868\u7684\u6240\u6709\u8a18\u9304\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-78908","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78908","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=78908"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78908\/revisions"}],"predecessor-version":[{"id":78909,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78908\/revisions\/78909"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=78908"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=78908"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=78908"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}