富贵资源网 Design By www.hznty.com

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):

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

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》

希望本文所述对大家MySQL数据库计有所帮助。

富贵资源网 Design By www.hznty.com
广告合作:本站广告合作请联系QQ:858582 申请时备注:广告合作(否则不回)
免责声明:本站资源来自互联网收集,仅供用于学习和交流,请遵循相关法律法规,本站一切资源不代表本站立场,如有侵权、后门、不妥请联系本站删除!
富贵资源网 Design By www.hznty.com

P70系列延期,华为新旗舰将在下月发布

3月20日消息,近期博主@数码闲聊站 透露,原定三月份发布的华为新旗舰P70系列延期发布,预计4月份上市。

而博主@定焦数码 爆料,华为的P70系列在定位上已经超过了Mate60,成为了重要的旗舰系列之一。它肩负着重返影像领域顶尖的使命。那么这次P70会带来哪些令人惊艳的创新呢?

根据目前爆料的消息来看,华为P70系列将推出三个版本,其中P70和P70 Pro采用了三角形的摄像头模组设计,而P70 Art则采用了与上一代P60 Art相似的不规则形状设计。这样的外观是否好看见仁见智,但辨识度绝对拉满。