mysql多個(gè)leftjoin連接查詢用法分析

來(lái)源：懂視網(wǎng) 責(zé)編：小采時(shí)間：2020-11-09 20:25:23

mysql多個(gè)leftjoin連接查詢用法分析

mysql多個(gè)leftjoin連接查詢用法分析:本文實(shí)例講述了mysql多個(gè)left join連接查詢用法。分享給大家供大家參考，具體如下： mysql查詢時(shí)需要連接多個(gè)表時(shí)，比如查詢訂單的商品表，需要查詢商品的其他信息，其他信息不在訂單的商品表，需要連接其他庫(kù)的表，但是連接的條件基本都是商品ID就可以了，

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導(dǎo)讀mysql多個(gè)leftjoin連接查詢用法分析:本文實(shí)例講述了mysql多個(gè)left join連接查詢用法。分享給大家供大家參考，具體如下： mysql查詢時(shí)需要連接多個(gè)表時(shí)，比如查詢訂單的商品表，需要查詢商品的其他信息，其他信息不在訂單的商品表，需要連接其他庫(kù)的表，但是連接的條件基本都是商品ID就可以了，

本文實(shí)例講述了mysql多個(gè)left join連接查詢用法。分享給大家供大家參考，具體如下：

mysql查詢時(shí)需要連接多個(gè)表時(shí)，比如查詢訂單的商品表，需要查詢商品的其他信息，其他信息不在訂單的商品表，需要連接其他庫(kù)的表，但是連接的條件基本都是商品ID就可以了，先給一個(gè)錯(cuò)誤語(yǔ)句（查詢之間的嵌套，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

查詢結(jié)果耗時(shí)4秒多，explain分析，發(fā)現(xiàn)其中2個(gè)子查詢是全部掃描，可以使用mysql的多個(gè)left join優(yōu)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

查詢結(jié)果耗時(shí)0.04秒

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