mysql多个left join

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）：

SELECTA.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(SELECTA.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 classifyFROMorder_goods AS ALEFT JOIN (SELECTA.goods_id,A.parentid,B.goods_nameFROMtest_qyg_goods.goods AS ALEFT JOIN test_qyg_goods.goods AS B ON A.parentid = B.goods_id) AS B ON A.goods_id = B.goods_idWHEREA.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 BYA.photo_idORDER BYA.goods_id ASC) AS A
LEFT JOIN (SELECTA.wid,A.brand_id,B.gb_nameFROMtest_qyg_user.buser_goods_list AS ALEFT 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

SELECTA.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(CASEWHEN F.buy_type = 'yes' THENA.numELSE0END) AS total_buy_num,sum(CASEWHEN F.buy_type = 'yes' THENA.numELSE0END * A.sell_price) AS total_buy_money,sum(CASEWHEN F.buy_type = 'no' THENA.numELSE0END) AS total_give_num,sum(CASEWHEN F.buy_type = 'no' THENA.numELSE0END * A.sell_price) AS total_give_money
FROMorder_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
WHEREA.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 BYA.photo_id
ORDER BYA.goods_id ASC

查询结果耗时0.04秒

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