mysql多个left join连接查询用法分析
网络 2018-07-16 1300
本文实例讲述了mysql多个left join连接查询用法。分享给大家供大家参考，具体如下：
mysql查询时需要连接多个表时，比如查询订单的商品表，需要查询商品的其他信息，其他信息不在订单的商品表，需要连接其他库的表，但是连接的条件基本都是商品ID就可以了，先给一个错误语句（查询之间的嵌套，效率很低）：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 | SELECT A.order_id, A.wid, A.work_name, A.supply_price, A.sell_price, A.total_num, A.sell_profit, A.sell_percent, A.goods_id, A.goods_name, A.classify, B.gb_name FROM ( SELECT A.sub_order_id AS order_id, A.photo_id AS wid, A.photo_name AS work_name, A.supply_price, A.sell_price, sum(A.num) AS total_num, ( A.sell_price - A.supply_price ) AS sell_profit, ( A.sell_price - A.supply_price ) / A.sell_price AS sell_percent, A.goods_id, A.goods_name, B.goods_name AS classify FROM order_goods AS A LEFT JOIN ( SELECT A.goods_id, A.parentid, B.goods_name FROM test_qyg_goods.goods AS A LEFT JOIN test_qyg_goods.goods AS B ON A.parentid = B.goods_id ) AS B ON A.goods_id = B.goods_id WHERE A.createtime >= '2016-09-09 00:00:00' AND A.createtime <= '2016-10-16 23:59:59' AND FROM_UNIXTIME( UNIX_TIMESTAMP(A.createtime), '%Y-%m-%d' ) != '2016-09-28' AND FROM_UNIXTIME( UNIX_TIMESTAMP(A.createtime), '%Y-%m-%d' ) != '2016-10-07' GROUP BY A.photo_id ORDER BY A.goods_id ASC ) AS A LEFT JOIN ( SELECT A.wid, A.brand_id, B.gb_name FROM test_qyg_user.buser_goods_list AS A LEFT JOIN test_qyg_supplier.brands AS B ON A.brand_id = B.gbid ) AS B ON A.wid = B.wid |
查询结果耗时4秒多，explain分析，发现其中2个子查询是全部扫描，可以使用mysql的多个left join优化
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 | SELECT A.sub_order_id, A.photo_id AS wid, A.photo_name AS work_name, A.supply_price, A.sell_price, sum(A.num) AS total_num, ( A.sell_price - A.supply_price ) AS sell_profit, ( A.sell_price - A.supply_price ) / A.sell_price AS sell_percent, A.goods_id, A.goods_name, B.parentid, C.goods_name AS classify, D.brand_id, E.gb_name, sum( CASE WHEN F.buy_type = 'yes' THEN A.num ELSE 0 END ) AS total_buy_num, sum( CASE WHEN F.buy_type = 'yes' THEN A.num ELSE 0 END * A.sell_price ) AS total_buy_money, sum( CASE WHEN F.buy_type = 'no' THEN A.num ELSE 0 END ) AS total_give_num, sum( CASE WHEN F.buy_type = 'no' THEN A.num ELSE 0 END * A.sell_price ) AS total_give_money FROM order_goods AS A LEFT JOIN test_qyg_goods.goods AS B ON A.goods_id = B.goods_id LEFT JOIN test_qyg_goods.goods AS C ON B.parentid = C.goods_id LEFT JOIN test_qyg_user.buser_goods_list AS D ON A.photo_id = D.wid LEFT JOIN test_qyg_supplier.brands AS E ON D.brand_id = E.gbid LEFT JOIN order_info_sub AS F ON A.sub_order_id = F.order_id WHERE A.createtime >= '2016-09-09 00:00:00' AND A.createtime <= '2016-10-16 23:59:59' AND FROM_UNIXTIME( UNIX_TIMESTAMP(A.createtime), '%Y-%m-%d' ) != '2016-09-28' AND FROM_UNIXTIME( UNIX_TIMESTAMP(A.createtime), '%Y-%m-%d' ) != '2016-10-07' GROUP BY A.photo_id ORDER BY A.goods_id ASC |
查询结果耗时0.04秒
更多关于MySQL相关内容感兴趣的读者可查看本站专题：《MySQL常用函数大汇总》、《MySQL日志操作技巧大全》、《MySQL事务操作技巧汇总》、《MySQL存储过程技巧大全》及《MySQL数据库锁相关技巧汇总》
