Question

我有一个sql一直给我一个异常，我无法弄清楚为什么，我的问题是avg（x.Points）由于某种原因返回null，在这种情况下如何让它返回0？

    UPDATE a
SET a.Points = (SELECT avg(x.Points) FROM 
   (SELECT TOP 5 * 
    FROM [dbo].[AlbumImages] i 
    WHERE i.AlbumId = a.Id 
    AND i.Points > 0 
    ORDER BY i.Points Desc) x)
FROM  [dbo].[Albums] a
    join [dbo].[Users] u on a.UserId = u.Id
WHERE u.DoRanking = 1

这给了我例外

Cannot insert the value NULL into column 'Points', 
table 'Cosplay.dbo.Albums'; column does not allow nulls. UPDATE fails.

Answer 1

您可以在AVG功能上查看ISNULL。当表达式为空时，ISNULL接受第二个参数返回。

UPDATE a
SET a.Points = (SELECT ISNULL(avg(x.Points),0) 
                FROM (SELECT TOP 5 * 
                      FROM [dbo].[AlbumImages] i 
                      WHERE i.AlbumId = a.Id 
                      AND i.Points > 0 
                      ORDER BY i.Points Desc) x)
FROM  [dbo].[Albums] a
    join [dbo].[Users] u on a.UserId = u.Id
WHERE u.DoRanking = 1

TSQL更新检查是否为null

1 个答案: