我使用的是SQL Server 2005，但遇到错误，我敢肯定应该不会得到。

Msg 512, Level 16, State 1, Procedure spGetSavedSearchesByAdminUser, Line 8 Subquery
returned more than 1 value. This is not permitted when the subquery
follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

我正在关注exampleB
此MSDN链接。

我存储的proc代码如下。如果我们要求的话，我可以为这篇文章简化它：

ALTER PROCEDURE [dbo].[spGetSavedSearchesByAdminUser] 
    @strUserName varchar(50)  
    ,@bitQuickSearch bit = 0
AS

BEGIN

    SELECT [intSearchID] ,strSearchTypeCode ,[strSearchName]
    FROM [tblAdminSearches] 

    WHERE 
        strUserName = @strUserName
        AND 
        strSearchTypeCode 
            IN (
                CASE @bitQuickSearch 
                WHEN 1 THEN 'Quick' 
                ELSE (SELECT strSearchTypeCode FROM tblAdvanceSearchTypes) 
                END
            )

    ORDER BY strSearchName
END

我检查了子查询的结果集与与子查询结果进行比较的strSearchTypeCode之间是否没有数据类型不匹配。

我看不出为什么这行不通。如果我们有任何线索，请告诉我。

解决方案

我不知道我们可以在IN子句中使用CASE语句。我建议将其重写为：

WHERE strUserName = @strUserName AND (
   (@bitQuickSearch = 1 AND strSearchTypeCode = 'Quick')
   OR
   (strSearchTypeCode IN (SELECT strSearchTypeCode FROM tblAdvanceSearchTypes))
)

或者，如果我们真的很喜欢那里的风格：

WHERE strUserName = @strUserName 
   AND strSearchTypeCode IN (
      SELECT CASE @bitQuickSearch WHEN 1 THEN 'Quick' ELSE strSearchTypeCode END
      FROM tblAdvanceSearchTypes
   )

通常，如果@bitQuickSearch = 1，则SQL应该足够聪明，足以优化表。但是，我只是为了确定(信任但要验证)检查查询计划。

在我看来，此SELECT：

SELECT strSearchTypeCode FROM tblAdvanceSearchTypes

返回多行，那是你的问题。我们可以将其重写为：

SELECT TOP 1 strSearchTypeCode FROM tblAdvanceSearchTypes

尝试重新排列查询，以便布尔表达式出现在子选择内部，例如

ALTER PROCEDURE [dbo].[spGetSavedSearchesByAdminUser] 
    @strUserName varchar(50)  
    ,@bitQuickSearch bit = 0
AS

BEGIN

    SELECT [intSearchID] ,strSearchTypeCode ,[strSearchName]
    FROM [tblAdminSearches] 

    WHERE 
        strUserName = @strUserName
        AND 
        strSearchTypeCode 
                IN (SELECT strSearchTypeCode FROM tblAdvanceSearchTypes where @bitQuickSearch=0
                    UNION
                    SELECT 'Quick' AS strSearchTypeCode WHERE @bitQuickSearch=1)

    ORDER BY strSearchName
END