Question

[authorityID] (TinyInt)列永远不会是null。

如果没有行，我想要的是返回15。通过下面的查询，如果没有行，我什么也得不到：

select top 1 isnull([authorityID],15) 
from [docAuthority] with (nolock) 
where [grpID] = 0 and [sID] = 42

Answer 1

SELECT  authorityId = isnull(( SELECT   [authorityID]
                               FROM     [docAuthority] WITH ( NOLOCK )
                               WHERE    [grpID] = 0
                                        AND [sID] = 42
                             ), 15)

Answer 2

如您所述，如果查询未返回任何行，则无法应用isnull。一个肮脏的技巧是使用union all和（ab）使用top构造：

SELECT TOP 1 authorityID
FROM   (SELECT authorityID
        FROM   [docAuthority] WITH (nolock) 
        WHERE  [grpID] = 0 AND [sID] = 42
        UNION ALL
        SELECT 15) t

如果没有行匹配则返回一个值

2 个答案: