Question

我的数据库中有2个表，表与外键有关系我想从主表中选择所有记录，然后选择另一个表中每行的计数，而不是主表中的相同ID我尝试创建一个选择查询，但它无法正常工作此查询返回主表中的所有记录+下一个表中所有记录的计数（不是关系中每一行的计数）

    SELECT tblForumSubGroups_1.id, tblForumSubGroups_1.GroupID,
    tblForumSubGroups_1.SubGroupTitle, tblForumSubGroups_1.SubGroupDesc,
    (SELECT COUNT(dbo.tblForumPosts.id) AS Expr1
    FROM dbo.tblForumSubGroups INNER JOIN dbo.tblForumPosts ON 
    dbo.tblForumSubGroups.id = dbo.tblForumPosts.SubGroupID) AS Expr1
    FROM dbo.tblForumSubGroups AS tblForumSubGroups_1 INNER JOIN
    dbo.tblForumPosts AS tblForumPosts_1 ON tblForumSubGroups_1.id 
    = tblForumPosts_1.SubGroupID

Answer 1

SELECT  tblForumSubGroups_1.id, tblForumSubGroups_1.GroupID, tblForumSubGroups_1.SubGroupTitle, tblForumSubGroups_1.SubGroupDesc,
        COUNT(tblForumPosts_1.id) AS Expr1
FROM    dbo.tblForumSubGroups AS tblForumSubGroups_1
INNER JOIN  dbo.tblForumPosts AS tblForumPosts_1 ON tblForumSubGroups_1.id = tblForumPosts_1.SubGroupID
GROUP BY tblForumSubGroups_1.id, tblForumSubGroups_1.GroupID, tblForumSubGroups_1.SubGroupTitle, tblForumSubGroups_1.SubGroupDesc

Answer 2

不要混合子查询和连接逻辑。只使用其中一个。我更喜欢子选择。

SELECT tblForumSubGroups_1.id,
       tblForumSubGroups_1.GroupID,
       tblForumSubGroups_1.SubGroupTitle,
       tblForumSubGroups_1.SubGroupDesc,
       (SELECT COUNT(*)
        FROM dbo.tblForumPosts
        WHERE dbo.tblForumSubGroups.id = dbo.tblForumPosts.SubGroupID) AS Expr1
FROM dbo.tblForumSubGroups AS tblForumSubGroups_1

Answer 3

我建议交叉申请，因为你可以用它做更多的事情......

SELECT t1.id,
   t1.GroupID,
   t1.SubGroupTitle,
   t1.SubGroupDesc,
   t2.val
FROM dbo.tblForumSubGroups AS t1
cross apply (SELECT COUNT(*)
         FROM dbo.tblForumPosts as t2
         WHERE t1.id = t2.SubGroupID) x(val)

Answer 4

只是提供另一个答案，但我相信交叉申请可能是最好的选择：

SELECT 
    A.id, A.GroupID, A.SubGroupTitle, A.SubGroupDesc,
    B.IDCount AS Expr1
FROM dbo.tblForumSubGroups A 
INNER JOIN (
    Select SubGroupID, Count(ID) as IDCount
    from dbo.tblForumPosts
    Group By SubGroupID
) B On A.ID = B.SubGroupID

从主表中选择记录和在另一个表中的每一行的计数

4 个答案: