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奥门金沙手机娱乐网址mysql多个left join连接查询用法分析

时间:2020-04-22 21:02来源:计算机
本文实例讲述了mysql多个leftjoin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

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:

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_nameFROM ( 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 ALEFT 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

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_moneyFROM order_goods AS ALEFT JOIN test_qyg_goods.goods AS B ON A.goods_id = B.goods_idLEFT JOIN test_qyg_goods.goods AS C ON B.parentid = C.goods_idLEFT JOIN test_qyg_user.buser_goods_list AS D ON A.photo_id = D.widLEFT JOIN test_qyg_supplier.brands AS E ON D.brand_id = E.gbidLEFT JOIN order_info_sub AS F ON A.sub_order_id = F.order_idWHERE 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_idORDER BY A.goods_id ASC

查询结果耗时0.04秒

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希望本文所述对大家MySQL数据库计有所帮助。

编辑:计算机 本文来源:奥门金沙手机娱乐网址mysql多个left join连接查询用法分析

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