\u4e8c\u3001 \u8054\u5408\u67e5\u8be2<\/p>\n
UNION\u8fd0\u7b97\u7b26\u53ef\u4ee5\u5c06\u4e24\u4e2a\u6216\u4e24\u4e2a\u4ee5\u4e0a\u4e0aSELECT\u8bed\u53e5\u7684\u67e5\u8be2\u7ed3\u679c\u96c6\u5408\u5408\u5e76\u6210\u4e00\u4e2a\u7ed3\u679c\u96c6\u5408\u663e\u793a\uff0c\u5373\u6267\u884c\u8054\u5408\u67e5\u8be2\u3002UNION\u7684\u8bed\u6cd5\u683c\u5f0f\u4e3a\uff1a<\/p>\n
select_statement
\nUNION [ALL] selectstatement
\n[UNION [ALL] selectstatement][\u2026n]<\/p>\n
\u5176\u4e2dselectstatement\u4e3a\u5f85\u8054\u5408\u7684SELECT\u67e5\u8be2\u8bed\u53e5\u3002<\/p>\n
ALL\u9009\u9879\u8868\u793a\u5c06\u6240\u6709\u884c\u5408\u5e76\u5230\u7ed3\u679c\u96c6\u5408\u4e2d\u3002\u4e0d\u6307\u5b9a\u8be5\u9879\u65f6\uff0c\u88ab\u8054\u5408\u67e5\u8be2\u7ed3\u679c\u96c6\u5408\u4e2d\u7684\u91cd\u590d\u884c\u5c06\u53ea\u4fdd\u7559\u4e00\u884c\u3002<\/p>\n
\u8054\u5408\u67e5\u8be2\u65f6\uff0c\u67e5\u8be2\u7ed3\u679c\u7684\u5217\u6807\u9898\u4e3a\u7b2c\u4e00\u4e2a\u67e5\u8be2\u8bed\u53e5\u7684\u5217\u6807\u9898\u3002\u56e0\u6b64\uff0c\u8981\u5b9a\u4e49\u5217\u6807\u9898\u5fc5\u987b\u5728\u7b2c\u4e00\u4e2a\u67e5\u8be2\u8bed\u53e5\u4e2d\u5b9a\u4e49\u3002\u8981\u5bf9\u8054\u5408\u67e5\u8be2\u7ed3\u679c\u6392\u5e8f\u65f6\uff0c\u4e5f\u5fc5\u987b\u4f7f\u7528\u7b2c\u4e00\u67e5\u8be2\u8bed\u53e5\u4e2d\u7684\u5217\u540d\u3001\u5217\u6807\u9898\u6216\u8005\u5217\u5e8f\u53f7\u3002<\/p>\n
\u5728\u4f7f\u7528UNION \u8fd0\u7b97\u7b26\u65f6\uff0c\u5e94\u4fdd\u8bc1\u6bcf\u4e2a\u8054\u5408\u67e5\u8be2\u8bed\u53e5\u7684\u9009\u62e9\u5217\u8868\u4e2d\u6709\u76f8\u540c\u6570\u91cf\u7684\u8868\u8fbe\u5f0f\uff0c\u5e76\u4e14\u6bcf\u4e2a\u67e5\u8be2\u9009\u62e9\u8868\u8fbe\u5f0f\u5e94\u5177\u6709\u76f8\u540c\u7684\u6570\u636e\u7c7b\u578b\uff0c\u6216\u662f\u53ef\u4ee5\u81ea\u52a8\u5c06\u5b83\u4eec\u8f6c\u6362\u4e3a\u76f8\u540c\u7684\u6570\u636e\u7c7b\u578b\u3002\u5728\u81ea\u52a8\u8f6c\u6362\u65f6\uff0c\u5bf9\u4e8e\u6570\u503c\u7c7b\u578b\uff0c\u7cfb\u7edf\u5c06\u4f4e\u7cbe\u5ea6\u7684\u6570\u636e\u7c7b\u578b\u8f6c\u6362\u4e3a\u9ad8\u7cbe\u5ea6\u7684\u6570\u636e\u7c7b\u578b\u3002<\/p>\n
\u5728\u5305\u62ec\u591a\u4e2a\u67e5\u8be2\u7684UNION\u8bed\u53e5\u4e2d\uff0c\u5176\u6267\u884c\u987a\u5e8f\u662f\u81ea\u5de6\u81f3\u53f3\uff0c\u4f7f\u7528\u62ec\u53f7\u53ef\u4ee5\u6539\u53d8\u8fd9\u4e00\u6267\u884c\u987a\u5e8f\u3002\u4f8b\u5982\uff1a<\/p>\n
\u67e5\u8be21 UNION (\u67e5\u8be22 UNION \u67e5\u8be23)<\/p>\n
\u4e09\u3001\u8fde\u63a5\u67e5\u8be2<\/p>\n
\u901a\u8fc7\u8fde\u63a5\u8fd0\u7b97\u7b26\u53ef\u4ee5\u5b9e\u73b0\u591a\u4e2a\u8868\u67e5\u8be2\u3002\u8fde\u63a5\u662f\u5173\u7cfb\u6570\u636e\u5e93\u6a21\u578b\u7684\u4e3b\u8981\u7279\u70b9\uff0c\u4e5f\u662f\u5b83\u533a\u522b\u4e8e\u5176\u5b83\u7c7b\u578b\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf\u7684\u4e00\u4e2a\u6807\u5fd7\u3002<\/p>\n
\u5728\u5173\u7cfb\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf\u4e2d\uff0c\u8868\u5efa\u7acb\u65f6\u5404\u6570\u636e\u4e4b\u95f4\u7684\u5173\u7cfb\u4e0d\u5fc5\u786e\u5b9a\uff0c\u5e38\u628a\u4e00\u4e2a\u5b9e\u4f53\u7684\u6240\u6709\u4fe1\u606f\u5b58\u653e\u5728\u4e00\u4e2a\u8868\u4e2d\u3002\u5f53\u68c0\u7d22\u6570\u636e\u65f6\uff0c\u901a\u8fc7\u8fde\u63a5\u64cd\u4f5c\u67e5\u8be2\u51fa\u5b58\u653e\u5728\u591a\u4e2a\u8868\u4e2d\u7684\u4e0d\u540c\u5b9e\u4f53\u7684\u4fe1\u606f\u3002\u8fde\u63a5\u64cd\u4f5c\u7ed9\u7528\u6237\u5e26\u6765\u5f88\u5927\u7684\u7075\u6d3b\u6027\uff0c\u4ed6\u4eec\u53ef\u4ee5\u5728\u4efb\u4f55\u65f6\u5019\u589e\u52a0\u65b0\u7684\u6570\u636e\u7c7b\u578b\u3002\u4e3a\u4e0d\u540c\u5b9e\u4f53\u521b\u5efa\u65b0\u7684\u8868\uff0c\u5c14\u540e\u901a\u8fc7\u8fde\u63a5\u8fdb\u884c\u67e5\u8be2\u3002<\/p>\n
\u8fde\u63a5\u53ef\u4ee5\u5728SELECT \u8bed\u53e5\u7684FROM\u5b50\u53e5\u6216WHERE\u5b50\u53e5\u4e2d\u5efa\u7acb\uff0c\u4f3c\u662f\u800c\u975e\u5728FROM\u5b50\u53e5\u4e2d\u6307\u51fa\u8fde\u63a5\u65f6\u6709\u52a9\u4e8e\u5c06\u8fde\u63a5\u64cd\u4f5c\u4e0eWHERE\u5b50\u53e5\u4e2d\u7684\u641c\u7d22\u6761\u4ef6\u533a\u5206\u5f00\u6765\u3002\u6240\u4ee5\uff0c\u5728Transact-SQL\u4e2d\u63a8\u8350\u4f7f\u7528\u8fd9\u79cd\u65b9\u6cd5\u3002<\/p>\n
SQL-92\u6807\u51c6\u6240\u5b9a\u4e49\u7684FROM\u5b50\u53e5\u7684\u8fde\u63a5\u8bed\u6cd5\u683c\u5f0f\u4e3a\uff1a<\/p>\n
FROM join_table join_type join_table
\n[ON (join_condition)]<\/p>\n
\u5176\u4e2djoin_table\u6307\u51fa\u53c2\u4e0e\u8fde\u63a5\u64cd\u4f5c\u7684\u8868\u540d\uff0c\u8fde\u63a5\u53ef\u4ee5\u5bf9\u540c\u4e00\u4e2a\u8868\u64cd\u4f5c\uff0c\u4e5f\u53ef\u4ee5\u5bf9\u591a\u8868\u64cd\u4f5c\uff0c\u5bf9\u540c\u4e00\u4e2a\u8868\u64cd\u4f5c\u7684\u8fde\u63a5\u53c8\u79f0\u505a\u81ea\u8fde\u63a5\u3002<\/p>\n
join_type \u6307\u51fa\u8fde\u63a5\u7c7b\u578b\uff0c\u53ef\u5206\u4e3a\u4e09\u79cd\uff1a\u5185\u8fde\u63a5\u3001\u5916\u8fde\u63a5\u548c\u4ea4\u53c9\u8fde\u63a5\u3002\u5185\u8fde\u63a5(INNER JOIN)\u4f7f\u7528\u6bd4\u8f83\u8fd0\u7b97\u7b26\u8fdb\u884c\u8868\u95f4\u67d0(\u4e9b)\u5217\u6570\u636e\u7684\u6bd4\u8f83\u64cd\u4f5c\uff0c\u5e76\u5217\u51fa\u8fd9\u4e9b\u8868\u4e2d\u4e0e\u8fde\u63a5\u6761\u4ef6\u76f8\u5339\u914d\u7684\u6570\u636e\u884c\u3002\u6839\u636e\u6240\u4f7f\u7528\u7684\u6bd4\u8f83\u65b9\u5f0f\u4e0d\u540c\uff0c\u5185\u8fde\u63a5\u53c8\u5206\u4e3a\u7b49\u503c\u8fde\u63a5\u3001\u81ea\u7136\u8fde\u63a5\u548c\u4e0d\u7b49\u8fde\u63a5\u4e09\u79cd\u3002\u5916\u8fde\u63a5\u5206\u4e3a\u5de6\u5916\u8fde\u63a5(LEFT OUTER JOIN\u6216LEFT JOIN)\u3001\u53f3\u5916\u8fde\u63a5(RIGHT OUTER JOIN\u6216RIGHT JOIN)\u548c\u5168\u5916\u8fde\u63a5(FULL OUTER JOIN\u6216FULL JOIN)\u4e09\u79cd\u3002\u4e0e\u5185\u8fde\u63a5\u4e0d\u540c\u7684\u662f\uff0c\u5916\u8fde\u63a5\u4e0d\u53ea\u5217\u51fa\u4e0e\u8fde\u63a5\u6761\u4ef6\u76f8\u5339\u914d\u7684\u884c\uff0c\u800c\u662f\u5217\u51fa\u5de6\u8868(\u5de6\u5916\u8fde\u63a5\u65f6)\u3001\u53f3\u8868(\u53f3\u5916\u8fde\u63a5\u65f6)\u6216\u4e24\u4e2a\u8868(\u5168\u5916\u8fde\u63a5\u65f6)\u4e2d\u6240\u6709\u7b26\u5408\u641c\u7d22\u6761\u4ef6\u7684\u6570\u636e\u884c\u3002<\/p>\n
\u4ea4\u53c9\u8fde\u63a5(CROSS JOIN)\u6ca1\u6709WHERE \u5b50\u53e5\uff0c\u5b83\u8fd4\u56de\u8fde\u63a5\u8868\u4e2d\u6240\u6709\u6570\u636e\u884c\u7684\u7b1b\u5361\u5c14\u79ef\uff0c\u5176\u7ed3\u679c\u96c6\u5408\u4e2d\u7684\u6570\u636e\u884c\u6570\u7b49\u4e8e\u7b2c\u4e00\u4e2a\u8868\u4e2d\u7b26\u5408\u67e5\u8be2\u6761\u4ef6\u7684\u6570\u636e\u884c\u6570\u4e58\u4ee5\u7b2c\u4e8c\u4e2a\u8868\u4e2d\u7b26\u5408\u67e5\u8be2\u6761\u4ef6\u7684\u6570\u636e\u884c\u6570\u3002<\/p>\n
\u8fde\u63a5\u64cd\u4f5c\u4e2d\u7684ON (join_condition) \u5b50\u53e5\u6307\u51fa\u8fde\u63a5\u6761\u4ef6\uff0c\u5b83\u7531\u88ab\u8fde\u63a5\u8868\u4e2d\u7684\u5217\u548c\u6bd4\u8f83\u8fd0\u7b97\u7b26\u3001\u903b\u8f91\u8fd0\u7b97\u7b26\u7b49\u6784\u6210\u3002<\/p>\n
\u65e0\u8bba\u54ea\u79cd\u8fde\u63a5\u90fd\u4e0d\u80fd\u5bf9text\u3001ntext\u548cimage\u6570\u636e\u7c7b\u578b\u5217\u8fdb\u884c\u76f4\u63a5\u8fde\u63a5\uff0c\u4f46\u53ef\u4ee5\u5bf9\u8fd9\u4e09\u79cd\u5217\u8fdb\u884c\u95f4\u63a5\u8fde\u63a5\u3002\u4f8b\u5982\uff1a<\/p>\n
SELECT p1.pub_id,p2.pub_id,p1.pr_info
\nFROM pub_info AS p1 INNER JOIN pub_info AS p2
\nON DATALENGTH(p1.pr_info)=DATALENGTH(p2.pr_info)<\/p>\n
(\u4e00)\u5185\u8fde\u63a5<\/p>\n
\u5185\u8fde\u63a5\u67e5\u8be2\u64cd\u4f5c\u5217\u51fa\u4e0e\u8fde\u63a5\u6761\u4ef6\u5339\u914d\u7684\u6570\u636e\u884c\uff0c\u5b83\u4f7f\u7528\u6bd4\u8f83\u8fd0\u7b97\u7b26\u6bd4\u8f83\u88ab\u8fde\u63a5\u5217\u7684\u5217\u503c\u3002\u5185\u8fde\u63a5\u5206\u4e09\u79cd\uff1a<\/p>\n
1\u3001\u7b49\u503c\u8fde\u63a5\uff1a\u5728\u8fde\u63a5\u6761\u4ef6\u4e2d\u4f7f\u7528\u7b49\u4e8e\u53f7(=)\u8fd0\u7b97\u7b26\u6bd4\u8f83\u88ab\u8fde\u63a5\u5217\u7684\u5217\u503c\uff0c\u5176\u67e5\u8be2\u7ed3\u679c\u4e2d\u5217\u51fa\u88ab\u8fde\u63a5\u8868\u4e2d\u7684\u6240\u6709\u5217\uff0c\u5305\u62ec\u5176\u4e2d\u7684\u91cd\u590d\u5217\u3002<\/p>\n
2\u3001\u4e0d\u7b49\u8fde\u63a5\uff1a \u5728\u8fde\u63a5\u6761\u4ef6\u4f7f\u7528\u9664\u7b49\u4e8e\u8fd0\u7b97\u7b26\u4ee5\u5916\u7684\u5176\u5b83\u6bd4\u8f83\u8fd0\u7b97\u7b26\u6bd4\u8f83\u88ab\u8fde\u63a5\u7684\u5217\u7684\u5217\u503c\u3002\u8fd9\u4e9b\u8fd0\u7b97\u7b26\u5305\u62ec>\u3001>=\u3001<=\u3001<\u3001!>\u3001!<\u548c<>\u3002<\/p>\n
3\u3001\u81ea\u7136\u8fde\u63a5\uff1a\u5728\u8fde\u63a5\u6761\u4ef6\u4e2d\u4f7f\u7528\u7b49\u4e8e(=)\u8fd0\u7b97\u7b26\u6bd4\u8f83\u88ab\u8fde\u63a5\u5217\u7684\u5217\u503c\uff0c\u4f46\u5b83\u4f7f\u7528\u9009\u62e9\u5217\u8868\u6307\u51fa\u67e5\u8be2\u7ed3\u679c\u96c6\u5408\u4e2d\u6240\u5305\u62ec\u7684\u5217\uff0c\u5e76\u5220\u9664\u8fde\u63a5\u8868\u4e2d\u7684\u91cd\u590d\u5217\u3002<\/p>\n
\u4f8b\uff0c\u4e0b\u9762\u4f7f\u7528\u7b49\u503c\u8fde\u63a5\u5217\u51faauthors\u548cpublishers\u8868\u4e2d\u4f4d\u4e8e\u540c\u4e00\u57ce\u5e02\u7684\u4f5c\u8005\u548c\u51fa\u7248\u793e\uff1a<\/p>\n
SELECT *
\nFROM authors AS a INNER JOIN publishers AS p
\nON a.city=p.city<\/p>\n
\u53c8\u5982\u4f7f\u7528\u81ea\u7136\u8fde\u63a5\uff0c\u5728\u9009\u62e9\u5217\u8868\u4e2d\u5220\u9664authors \u548cpublishers \u8868\u4e2d\u91cd\u590d\u5217(city\u548cstate)\uff1a<\/p>\n
SELECT a.*,p.pub_id,p.pub_name,p.country
\nFROM authors AS a INNER JOIN publishers AS p
\nON a.city=p.city<\/p>\n
(\u4e8c)\u5916\u8fde\u63a5<\/p>\n
\u5185\u8fde\u63a5\u65f6\uff0c\u8fd4\u56de\u67e5\u8be2\u7ed3\u679c\u96c6\u5408\u4e2d\u7684\u4ec5\u662f\u7b26\u5408\u67e5\u8be2\u6761\u4ef6( WHERE \u641c\u7d22\u6761\u4ef6\u6216 HAVING \u6761\u4ef6)\u548c\u8fde\u63a5\u6761\u4ef6\u7684\u884c\u3002\u800c\u91c7\u7528\u5916\u8fde\u63a5\u65f6\uff0c\u5b83\u8fd4\u56de\u5230\u67e5\u8be2\u7ed3\u679c\u96c6\u5408\u4e2d\u7684\u4e0d\u4ec5\u5305\u542b\u7b26\u5408\u8fde\u63a5\u6761\u4ef6\u7684\u884c\uff0c\u800c\u4e14\u8fd8\u5305\u62ec\u5de6\u8868(\u5de6\u5916\u8fde\u63a5\u65f6)\u3001\u53f3\u8868(\u53f3\u5916\u8fde\u63a5\u65f6)\u6216\u4e24\u4e2a\u8fb9\u63a5\u8868(\u5168\u5916\u8fde\u63a5)\u4e2d\u7684\u6240\u6709\u6570\u636e\u884c\u3002\u5982\u4e0b\u9762\u4f7f\u7528\u5de6\u5916\u8fde\u63a5\u5c06\u8bba\u575b\u5185\u5bb9\u548c\u4f5c\u8005\u4fe1\u606f\u8fde\u63a5\u8d77\u6765\uff1a<\/p>\n
SELECT a.*,b.* FROM luntan LEFT JOIN usertable as b
\nON a.username=b.username<\/p>\n
\u4e0b\u9762\u4f7f\u7528\u5168\u5916\u8fde\u63a5\u5c06city\u8868\u4e2d\u7684\u6240\u6709\u4f5c\u8005\u4ee5\u53causer\u8868\u4e2d\u7684\u6240\u6709\u4f5c\u8005\uff0c\u4ee5\u53ca\u4ed6\u4eec\u6240\u5728\u7684\u57ce\u5e02\uff1a<\/p>\n
SELECT a.*,b.*
\nFROM city as a FULL OUTER JOIN user as b
\nON a.username=b.username<\/p>\n
(\u4e09)\u4ea4\u53c9\u8fde\u63a5<\/p>\n
\u4ea4\u53c9\u8fde\u63a5\u4e0d\u5e26WHERE \u5b50\u53e5\uff0c\u5b83\u8fd4\u56de\u88ab\u8fde\u63a5\u7684\u4e24\u4e2a\u8868\u6240\u6709\u6570\u636e\u884c\u7684\u7b1b\u5361\u5c14\u79ef\uff0c\u8fd4\u56de\u5230\u7ed3\u679c\u96c6\u5408\u4e2d\u7684\u6570\u636e\u884c\u6570\u7b49\u4e8e\u7b2c\u4e00\u4e2a\u8868\u4e2d\u7b26\u5408\u67e5\u8be2\u6761\u4ef6\u7684\u6570\u636e\u884c\u6570\u4e58\u4ee5\u7b2c\u4e8c\u4e2a\u8868\u4e2d\u7b26\u5408\u67e5\u8be2\u6761\u4ef6\u7684\u6570\u636e\u884c\u6570\u3002\u4f8b\uff0ctitles\u8868\u4e2d\u67096\u7c7b\u56fe\u4e66\uff0c\u800cpublishers\u8868\u4e2d\u67098\u5bb6\u51fa\u7248\u793e\uff0c\u5219\u4e0b\u5217\u4ea4\u53c9\u8fde\u63a5\u68c0\u7d22\u5230\u7684\u8bb0\u5f55\u6570\u5c06\u7b49\u4e8e6*8=48\u884c\u3002<\/p>\n
SELECT type,pub_name
\nFROM titles CROSS JOIN publishers
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