为什么SQL情况下条件给出错误

Question

我做这样的事情的正常工作：

select nameOfCols 
from 
FACost 
inner join FAT as D on d.nid=a.atypeid 
and 
d.nid in (select item from SplitString('1,2,3,',',')) 

但是当我使用情况来处理的情况下用户可以动态地“而不是“1,2,3输入”， ”。然后提示错误在我的情况条件

declare @selectedAssetTypeID varchar(50)='1,2,3,' 
select nameOfCols 
from 
FACost 
inner join FAT as D on d.nid=a.atypeid 
and 
case when @selectedAssetTypeID<>'' then d.nid in (select item from SplitString(@selectedAssetTypeID,',')) else d.nid=1 end  //error causing lines 

错误是：

Msg 156, Level 15, State 1, Line 33 
Incorrect syntax near the keyword 'in'. 
Msg 156, Level 15, State 1, Line 33 
Incorrect syntax near the keyword 'else'. 

Answer 1

使用and和or条件，而不是case表达。您所拥有的case表达式是分配值（else d.nid=1）或检查真/假条件（d.nid in (select item from SplitString(@selectedAssetTypeID,','))）。

and (
(@selectedAssetTypeID <>'' and d.nid in (select item from SplitString(@selectedAssetTypeID,','))) 
or (d.nid=1) 
) 

Answer 2

不能使用in子句case声明。因为Case必须为每个语句返回一个值（无论是true还是false）

要么您可以将查询分成两个块，要么可以使用“OR”子句。

IF @selectedAssetTypeID = " " 
BEGIN 
    select nameOfCols 
    from FACost 
    inner join FAT as D 
     on (d.nid = a.atypeid) 
    where d.nid = 1 
END 
ELSE 
BEGIN 
    select nameOfCols 
    from FACost 
    inner join FAT as D 
     on (d.nid = a.atypeid) 
    where d.nid IN 
    (select item from SplitString(@selectedAssetTypeID,',')) 
END 

您还可以使用 “OR” 条款

select nameOfCols 
    from FACost 
    inner join FAT as D 
     on (d.nid = a.atypeid) 
    where ((@selectedAssetTypeID <>'' and d.nid in (select item from SplitString(@selectedAssetTypeID,','))) 
or (d.nid=1)) 

链接，关于类似问题的讨论低于

https://social.msdn.microsoft.com/Forums/sqlserver/en-US/bc8a7a0b-1980-4481-a2df-6a5fde38f362/in-clause-in-case-statement?forum=sqlgetstarted