Question

我正在尝试传入参数，如果参数为null，我想将县Id设置为自己。如果县Id不为空，那么我想带回县合作中所有县的记录。

我的语法错误不正确。关于如何做到这一点的任何想法？

    DECLARE @pCountyId as int;

    select  p.Id, p.LastName, p.FirstName, c.Id, c.Description
    FROM Participant as p
    INNER JOIN Application as a on p.Id = a.ParticipantId
    INNER JOIN Dictionary.Counties as c on a.CountyId = c.Id
    WHERE 

    If @pCountyId is null 
        BEGIN
            c.Id = c.Id
        END
    ELSE
            c.Id in (SELECT cc.CountyId 
                    FROM CountyCollaboration as cc
                    WHERE cc.CollaborationId = (SELECT cc1.CollaborationId 
                                       FROM CountyCollaboration as cc1
                                       WHERE cc1.CountyId = @pCountyId))

Answer 1

尝试：

WHERE 

(@pCountyId is null) OR 

c.Id in (SELECT cc.CountyId 
                    FROM CountyCollaboration as cc
                    WHERE cc.CollaborationId = (SELECT cc1.CollaborationId 
                                       FROM CountyCollaboration as cc1
                                       WHERE cc1.CountyId = @pCountyId))

但是要重新考虑你的情况，这是太多的子查询。

Answer 2

据我所知，你不能以你在查询中的方式添加if语句 - 没有这种查询的语法。您可以使用每个块中的两个单独查询完成您正在执行的操作（复制SELECT / INNER JOIN），但它不是最理想的解决方案。

Answer 3

这应该是你：

select  p.Id        ,
        p.LastName  ,
        p.FirstName ,
        c.Id ,
        c.Description
from Participant         p
join Application         a on a.ParticipantId = p.Id
join Dictionary.Counties c on c.Id            = a.CountyId
where       @pCountyId is     null
   OR (     @pCountyID is not null
        and c.Id in ( select cc.CountyId 
                      from CountyCollaboration cc
                      join CountyCollaboration cc1 on cc1.CollaborationId = cc.CollaborationId
                                                  and cc1.CountID = @pCountyId
                    )
      )

sql if语句检查null参数

3 个答案: