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我有以下 SQL 查询。

SELECT    u.username, SUM(p.points) AS points,
          SUM(sp.spPoints) AS spPoints,
          (SUM(sp.spPoints) - SUM(p.points)) AS Puntos_Restantes
FROM      users as u
LEFT JOIN points as p ON (u.userid = p.userid)
LEFT JOIN sppoints AS sp ON (u.userid = sp.userid)
WHERE     u.userid = '1'
GROUP BY  u.userid

我的目标是求和 2 个字段，然后减去它们，但是当我执行上述查询时，第二个 SUM 是错误的。
表格是这样的： 

points: pointId, userId, points    
sppoints: spPointId, userId, spPoints

在点我有这个数量：25 和 spPoints：10 但是当我运行查询时，我得到：

points  spPoints    Puntos_Restantes
 25       30              5

这里出了什么问题？

4

1 回答 1

2

该表users与其他 2 个表具有一对多关系。这会导致 2 个连接产生一个 mini-Carstesian 积和多行在列中具有相同数据的points行 - 然后将其聚合。

您可以使用子查询进行分组，然后加入，以避免此问题：

SELECT 
      u.username
    , COALESCE(p.pPoints,0) 
        AS pPoints
    , COALESCE(sp.spPoints,0) 
        AS spPoints
    , COALESCE(p.pPoints,0) - COALESCE(sp.spPoints,0)
        AS Puntos_Restantes
FROM 
      users as u
  LEFT JOIN 
      ( SELECT userid, SUM(points) AS pPoints
        FROM points
        WHERE userid = 1
        GROUP BY userid
      ) AS p
    ON u.userid = p.userid
  LEFT JOIN 
      ( SELECT userid, SUM(spPoints) AS spPoints
        FROM sppoints
        WHERE userid = 1
        GROUP BY userid
      ) AS sp
    ON u.userid = sp.userid
WHERE u.userid = 1 ;

如果您想获得多个用户（或所有用户）的结果，请替换这三个WHERE userid=1条件（或完全删除它们）。

指数将有助于提高效率points(userid, points)。sppoints(userid, spPoints)

于 2012-07-05T14:03:27.133 回答