{"id":158761,"date":"2024-11-03T04:35:24","date_gmt":"2024-11-02T20:35:24","guid":{"rendered":"https:\/\/server.hk\/cnblog\/158761\/"},"modified":"2024-11-03T04:35:25","modified_gmt":"2024-11-02T20:35:25","slug":"%e9%97%9c%e6%96%bc-hivesql-%e5%b8%b8%e8%a6%8b%e7%9a%84-left-join-%e8%aa%a4%e5%8d%80%ef%bc%8c%e4%bd%a0%e7%9f%a5%e9%81%93%e5%97%8e","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/158761\/","title":{"rendered":"\u95dc\u65bc HiveSQL \u5e38\u898b\u7684 Left Join \u8aa4\u5340\uff0c\u4f60\u77e5\u9053\u55ce"},"content":{"rendered":"<h1 id=\"%e9%97%9c%e6%96%bc-hivesql-%e5%b8%b8%e8%a6%8b%e7%9a%84-left-join-%e8%aa%a4%e5%8d%80%ef%bc%8c%e4%bd%a0%e7%9f%a5%e9%81%93%e5%97%8e-fkQrFTdKXP\">\u95dc\u65bc HiveSQL \u5e38\u898b\u7684 Left Join \u8aa4\u5340\uff0c\u4f60\u77e5\u9053\u55ce<\/h1>\n<p>\u5728\u5927\u6578\u64da\u8655\u7406\u548c\u5206\u6790\u7684\u9818\u57df\u4e2d\uff0cHiveSQL \u4f5c\u70ba\u4e00\u7a2e\u6d41\u884c\u7684\u67e5\u8a62\u8a9e\u8a00\uff0c\u5ee3\u6cdb\u61c9\u7528\u65bc Hadoop \u751f\u614b\u7cfb\u7d71\u4e2d\u3002\u5b83\u7684\u8a9e\u6cd5\u985e\u4f3c\u65bc SQL\uff0c\u4e26\u4e14\u80fd\u5920\u8655\u7406\u5927\u91cf\u7684\u6578\u64da\u3002\u7136\u800c\uff0c\u5728\u4f7f\u7528 HiveSQL \u9032\u884c\u6578\u64da\u67e5\u8a62\u6642\uff0c\u8a31\u591a\u7528\u6236\u5728\u4f7f\u7528 <code>LEFT JOIN<\/code> \u6642\u5e38\u5e38\u6703\u9047\u5230\u4e00\u4e9b\u8aa4\u5340\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u9019\u4e9b\u8aa4\u5340\uff0c\u5e6b\u52a9\u8b80\u8005\u66f4\u597d\u5730\u7406\u89e3\u548c\u4f7f\u7528 HiveSQL \u7684 <code>LEFT JOIN<\/code>\u3002<\/p>\n<h2 id=\"%e4%bb%80%e9%ba%bc%e6%98%af-left-join-fkQrFTdKXP\">\u4ec0\u9ebc\u662f LEFT JOIN<\/h2>\n<p><code>LEFT JOIN<\/code> \u662f\u4e00\u7a2e\u806f\u63a5\u64cd\u4f5c\uff0c\u4e3b\u8981\u7528\u65bc\u5f9e\u5de6\u8868\u4e2d\u9078\u53d6\u6240\u6709\u7684\u8a18\u9304\uff0c\u4e26\u4e14\u5f9e\u53f3\u8868\u4e2d\u9078\u53d6\u7b26\u5408\u689d\u4ef6\u7684\u8a18\u9304\u3002\u5982\u679c\u53f3\u8868\u4e2d\u6c92\u6709\u7b26\u5408\u689d\u4ef6\u7684\u8a18\u9304\uff0c\u5247\u7d50\u679c\u4e2d\u6703\u986f\u793a\u5de6\u8868\u7684\u8a18\u9304\uff0c\u4e26\u4e14\u53f3\u8868\u7684\u6b04\u4f4d\u6703\u986f\u793a\u70ba <code>NULL<\/code>\u3002<\/p>\n<h2 id=\"%e5%b8%b8%e8%a6%8b%e7%9a%84-left-join-%e8%aa%a4%e5%8d%80-fkQrFTdKXP\">\u5e38\u898b\u7684 LEFT JOIN \u8aa4\u5340<\/h2>\n<h3 id=\"%e8%aa%a4%e5%8d%80%e4%b8%80%ef%bc%9a%e8%aa%a4%e8%a7%a3-left-join-%e7%9a%84%e7%b5%90%e6%9e%9c%e9%9b%86-fkQrFTdKXP\">\u8aa4\u5340\u4e00\uff1a\u8aa4\u89e3 LEFT JOIN \u7684\u7d50\u679c\u96c6<\/h3>\n<p>\u8a31\u591a\u521d\u5b78\u8005\u5728\u4f7f\u7528 <code>LEFT JOIN<\/code> \u6642\uff0c\u5e38\u5e38\u8aa4\u4ee5\u70ba\u7d50\u679c\u96c6\u53ea\u6703\u5305\u542b\u5de6\u8868\u7684\u6240\u6709\u8a18\u9304\u3002\u5be6\u969b\u4e0a\uff0c<code>LEFT JOIN<\/code> \u6703\u6839\u64da\u806f\u63a5\u689d\u4ef6\u5f9e\u53f3\u8868\u4e2d\u9078\u53d6\u7b26\u5408\u689d\u4ef6\u7684\u8a18\u9304\u3002\u5982\u679c\u53f3\u8868\u4e2d\u6c92\u6709\u7b26\u5408\u689d\u4ef6\u7684\u8a18\u9304\uff0c\u5247\u8a72\u884c\u7684\u53f3\u8868\u6b04\u4f4d\u6703\u986f\u793a\u70ba <code>NULL<\/code>\u3002\u4f8b\u5982\uff1a<\/p>\n<pre><code>SELECT a.id, a.name, b.salary\nFROM employees a\nLEFT JOIN salaries b ON a.id = b.emp_id;<\/code><\/pre>\n<p>\u5728\u9019\u500b\u67e5\u8a62\u4e2d\uff0c\u6240\u6709\u7684\u54e1\u5de5\u90fd\u6703\u88ab\u5217\u51fa\uff0c\u5373\u4f7f\u67d0\u4e9b\u54e1\u5de5\u5728\u85aa\u8cc7\u8868\u4e2d\u6c92\u6709\u5c0d\u61c9\u7684\u8a18\u9304\uff0c\u4ed6\u5011\u7684\u85aa\u8cc7\u6b04\u4f4d\u5c07\u986f\u793a\u70ba <code>NULL<\/code>\u3002<\/p>\n<h3 id=\"%e8%aa%a4%e5%8d%80%e4%ba%8c%ef%bc%9a%e5%bf%bd%e7%95%a5-null-%e5%80%bc%e7%9a%84%e8%99%95%e7%90%86-fkQrFTdKXP\">\u8aa4\u5340\u4e8c\uff1a\u5ffd\u7565 NULL \u503c\u7684\u8655\u7406<\/h3>\n<p>\u5728\u4f7f\u7528 <code>LEFT JOIN<\/code> \u6642\uff0c\u7d50\u679c\u96c6\u4e2d\u7684 <code>NULL<\/code> \u503c\u53ef\u80fd\u6703\u5f71\u97ff\u5f8c\u7e8c\u7684\u6578\u64da\u8655\u7406\u548c\u5206\u6790\u3002\u8a31\u591a\u7528\u6236\u5728\u9032\u884c\u6578\u64da\u8a08\u7b97\u6642\uff0c\u672a\u80fd\u8003\u616e\u5230\u9019\u4e9b <code>NULL<\/code> \u503c\uff0c\u5c0e\u81f4\u8a08\u7b97\u7d50\u679c\u4e0d\u6e96\u78ba\u3002\u56e0\u6b64\uff0c\u5728\u9032\u884c\u8a08\u7b97\u4e4b\u524d\uff0c\u61c9\u8a72\u5148\u8655\u7406\u9019\u4e9b <code>NULL<\/code> \u503c\uff0c\u4f8b\u5982\u4f7f\u7528 <code>COALESCE<\/code> \u51fd\u6578\u4f86\u66ff\u63db <code>NULL<\/code> \u503c\uff1a<\/p>\n<pre><code>SELECT a.id, a.name, COALESCE(b.salary, 0) AS salary\nFROM employees a\nLEFT JOIN salaries b ON a.id = b.emp_id;<\/code><\/pre>\n<p>\u9019\u6a23\u53ef\u4ee5\u78ba\u4fdd\u5728\u8a08\u7b97\u6642\u4e0d\u6703\u56e0\u70ba <code>NULL<\/code> \u503c\u800c\u5f71\u97ff\u7d50\u679c\u3002<\/p>\n<h3 id=\"%e8%aa%a4%e5%8d%80%e4%b8%89%ef%bc%9a%e4%b8%8d%e6%ad%a3%e7%a2%ba%e7%9a%84%e8%81%af%e6%8e%a5%e6%a2%9d%e4%bb%b6-fkQrFTdKXP\">\u8aa4\u5340\u4e09\uff1a\u4e0d\u6b63\u78ba\u7684\u806f\u63a5\u689d\u4ef6<\/h3>\n<p>\u5728\u4f7f\u7528 <code>LEFT JOIN<\/code> \u6642\uff0c\u6b63\u78ba\u7684\u806f\u63a5\u689d\u4ef6\u81f3\u95dc\u91cd\u8981\u3002\u5982\u679c\u806f\u63a5\u689d\u4ef6\u4e0d\u6b63\u78ba\uff0c\u53ef\u80fd\u6703\u5c0e\u81f4\u610f\u5916\u7684\u7d50\u679c\u96c6\u3002\u4f8b\u5982\uff0c\u5982\u679c\u806f\u63a5\u689d\u4ef6\u4f7f\u7528\u4e86\u932f\u8aa4\u7684\u6b04\u4f4d\uff0c\u5247\u53ef\u80fd\u6703\u5c0e\u81f4\u7d50\u679c\u96c6\u4e2d\u7684\u91cd\u8907\u8a18\u9304\u6216\u7f3a\u5931\u8a18\u9304\u3002\u56e0\u6b64\uff0c\u5728\u64b0\u5beb\u67e5\u8a62\u6642\uff0c\u61c9\u4ed4\u7d30\u6aa2\u67e5\u806f\u63a5\u689d\u4ef6\u7684\u6b63\u78ba\u6027\u3002<\/p>\n<h2 id=\"%e7%b5%90%e8%ab%96-fkQrFTdKXP\">\u7d50\u8ad6<\/h2>\n<p>\u5728\u4f7f\u7528 HiveSQL \u7684 <code>LEFT JOIN<\/code> \u6642\uff0c\u4e86\u89e3\u5e38\u898b\u7684\u8aa4\u5340\u53ef\u4ee5\u5e6b\u52a9\u7528\u6236\u66f4\u6709\u6548\u5730\u9032\u884c\u6578\u64da\u67e5\u8a62\u548c\u5206\u6790\u3002\u6b63\u78ba\u7406\u89e3 <code>LEFT JOIN<\/code> \u7684\u7d50\u679c\u96c6\u3001\u59a5\u5584\u8655\u7406 <code>NULL<\/code> \u503c\u4ee5\u53ca\u78ba\u4fdd\u806f\u63a5\u689d\u4ef6\u7684\u6b63\u78ba\u6027\uff0c\u90fd\u662f\u63d0\u9ad8\u67e5\u8a62\u6e96\u78ba\u6027\u7684\u91cd\u8981\u6b65\u9a5f\u3002<\/p>\n<p>\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u8655\u7406\u548c\u5206\u6790\u6709\u66f4\u9ad8\u7684\u9700\u6c42\uff0c\u8003\u616e\u4f7f\u7528 <a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a> \u4f86\u642d\u5efa\u60a8\u7684\u6578\u64da\u74b0\u5883\uff0c\u4eab\u53d7\u66f4\u9ad8\u6548\u7684\u6578\u64da\u8655\u7406\u80fd\u529b\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u63a2\u7d22 HiveSQL \u4e2d\u5e38\u898b\u7684 Left Join \u8aa4\u5340\uff0c\u4e86\u89e3\u5982\u4f55\u907f\u514d\u5e38\u898b\u932f\u8aa4\uff0c\u63d0\u5347\u67e5\u8a62\u6548\u7387\u8207\u6e96\u78ba\u6027\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-158761","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/158761","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=158761"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/158761\/revisions"}],"predecessor-version":[{"id":158762,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/158761\/revisions\/158762"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=158761"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=158761"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=158761"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}