Question

我收到此错误（请参阅标题）。我该如何纠正这个：

SQL

use adventureworks
go

select si.CustomerID,
'myField' =
            CASE
                 When (Select Top 1 FirstName,LastName  From Person.Contact pc Where si.ContactID = pc.contactid ) is not null Then 
            Cast((Select Top 1 FirstName,LastName  From Person.Contact pc Where si.ContactID = pc.contactid  ) As varchar)
            Else ''
            END
from Sales.Individual si
where si.CustomerID=11000

Answer 1

您正在尝试选择两个值并将它们视为一个表达式：

select top 1 FirstName, LastName ...

这可能应该改为这样：

select top 1 FirstName + ' ' + LastName ...

功能齐全的版本将是这样的：

select
    si.CustomerID,
    CASE
       WHEN
           (Select Top 1 FirstName + ' ' + LastName  From Person.Contact pc Where si.ContactID = pc.contactid ) is not null
       THEN
           (Select Top 1 FirstName + ' ' + LastName  From Person.Contact pc Where si.ContactID = pc.contactid  )
        Else ''
    END [myField]
from
    Sales.Individual si
where
    si.CustomerID=11000

Answer 2

修改查询

use adventureworks go  

select si.CustomerID, 'myField' =             
      CASE    When 
          (Select Top 1 FirstName From Person.Contact pc Where si.ContactID = pc.contactid ) is not null 
              Then              
          Cast((Select Top 1 FirstName
                   From Person.Contact pc Where si.ContactID = pc.contactid  ) As varchar)             
              Else ''             
     END from Sales.Individual si where si.CustomerID=11000

错误是因为你选择了FirstName和LastName，所以要删除错误选择其中一个firstanme或lastname或两者合二为一个

例如

Select Top 1 FirstName+ ' ' + LastName as fullName
                       From Person.Contact pc Where si.ContactID = pc.

这将解决您的问题

更多详细检查：Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.

Answer 3

在查询中使用子查询时，SQL只能从一个记录返回一个字段。您可能想要连接这些字段，您可以这样做：

use adventureworks
go

select si.CustomerID,
'myField' =
            CASE
                 When (Select Top 1 FirstName+ ' ' + LastName  From Person.Contact pc Where si.ContactID = pc.contactid ) is not null Then 
            Cast((Select Top 1 FirstName+ ' ' + LastName  From Person.Contact pc Where si.ContactID = pc.contactid  ) As varchar)
            Else ''
            END
from Sales.Individual si
where si.CustomerID=11000

或者你可以在子查询中选择其中一个字段。

sql错误：只能在选择列表中指定一个表达式？

3 个答案: