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。

标签:
mysql,left,join,连接查询

免责声明:本站文章均来自网站采集或用户投稿,网站不提供任何软件下载或自行开发的软件! 如有用户或公司发现本站内容信息存在侵权行为,请邮件告知! 858582#qq.com
白云城资源网 Copyright www.dyhadc.com

评论“mysql多个left join连接查询用法分析”

暂无“mysql多个left join连接查询用法分析”评论...

《魔兽世界》大逃杀!60人新游玩模式《强袭风暴》3月21日上线

暴雪近日发布了《魔兽世界》10.2.6 更新内容,新游玩模式《强袭风暴》即将于3月21 日在亚服上线,届时玩家将前往阿拉希高地展开一场 60 人大逃杀对战。

艾泽拉斯的冒险者已经征服了艾泽拉斯的大地及遥远的彼岸。他们在对抗世界上最致命的敌人时展现出过人的手腕,并且成功阻止终结宇宙等级的威胁。当他们在为即将于《魔兽世界》资料片《地心之战》中来袭的萨拉塔斯势力做战斗准备时,他们还需要在熟悉的阿拉希高地面对一个全新的敌人──那就是彼此。在《巨龙崛起》10.2.6 更新的《强袭风暴》中,玩家将会进入一个全新的海盗主题大逃杀式限时活动,其中包含极高的风险和史诗级的奖励。

《强袭风暴》不是普通的战场,作为一个独立于主游戏之外的活动,玩家可以用大逃杀的风格来体验《魔兽世界》,不分职业、不分装备(除了你在赛局中捡到的),光是技巧和战略的强弱之分就能决定出谁才是能坚持到最后的赢家。本次活动将会开放单人和双人模式,玩家在加入海盗主题的预赛大厅区域前,可以从强袭风暴角色画面新增好友。游玩游戏将可以累计名望轨迹,《巨龙崛起》和《魔兽世界:巫妖王之怒 经典版》的玩家都可以获得奖励。