Question

我有一个非常简单和自我解释的SQL语句：

ALTER PROCEDURE [dbo].[sp_getAllDebatesForAlias](@SubjectAlias nchar(30))
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    -- Insert statements for procedure here
    SELECT *
    FROM tblDebates
    WHERE (SubjectID1 in (SELECT SubjectID FROM tblSubjectAlias WHERE SubjectAlias = @SubjectAlias)) 
        OR (SubjectID2 in (SELECT SubjectID FROM tblSubjectAlias WHERE SubjectAlias = @SubjectAlias)) ;
END

我确信有一种方法可以使这个陈述更有效率，至少可以摆脱in部分中同一个表的多次创建，即

SELECT SubjectID FROM tblSubjectAlias WHERE SubjectAlias = @SubjectAlias

一部分。

有什么想法吗？

Answer 1

SELECT d.*
FROM tblDebates d
inner join tblSubjectAlias s on s.SubjectID in (d.SubjectID1, d.SubjectID2)
where s.SubjectAlias = @SubjectAlias

Answer 2

尝试：

select d.* from tblDebates d
where exists
(select 1
 from tblSubjectAlias s
 where s.SubjectID in (d.SubjectID1, d.SubjectID2) and
       s.SubjectAlias = @SubjectAlias)

避免在SQL中两次创建相同的查询

2 个答案: