mysql多个left join

秒速五厘米 2022-07-16 11:47 141阅读 0赞

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）：

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

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