SQL中的选择内连接选择

Posted 2023-05-08

【中文标题】SQL中的选择内连接选择

【英文标题】：Select Inner Join Select in SQL

【发布时间】：2015-05-21 02:29:24

【问题描述】：

您好，我有一个 Select Inner Join 语句，看起来没问题，但我出错了。这是我的查询

ALTER PROCEDURE [dbo].[POBalance]  @PONumber nvarchar(50)
AS BEGIN
Select( 
Select 
    A.Description,
    C.qty as POqty,
    B.QtyDelivered as PDQty, 
    case when A.partialflag ='false' 
    then '0'
    else
    A.qty  end as Balance,
    A.Unit,
    A.Unitprice,
    A.Partialflag 
from tblPOdetails as A

Inner Join  ( SELECT  id, SUM(Qty) AS QtyDelivered
                                    FROM         dbo.tblPDdetails
                                    WHERE     (PONo = @PONumber)
                                    GROUP BY id)as B On A.id = B.id   
Inner Join tblpodetailshistory as C on A.id =C.id

where A.PONo = @PONumber)
END

我收到了这个错误。

选择列表中只能指定一个表达式，当 EXISTS 没有引入子查询。

在此先感谢您。

【问题讨论】：

错误信息非常具体地解释了问题是什么以及解决方案将是什么。用非常清晰的措辞您是否阅读了错误信息中的实际文字？哪一部分不清楚？

@KenWhite 对不起，我是新手，SQL 我只想在我的第一个表上加入 Qtydelivered ......当我运行子查询时，它似乎没问题。谢谢。

【参考方案1】：

您应该在外部选择语句中包含列名和 From 关键字

ALTER PROCEDURE [dbo].[POBalance]  @PONumber nvarchar(50)
AS BEGIN
Select Description, POqty, PDQty, Balance, Unit, Unitprice, Partialflag  from ( 
Select 
    A.Description,
    C.qty as POqty,
    B.QtyDelivered as PDQty, 
    case when A.partialflag ='false' 
    then '0'
    else
    A.qty  end as Balance,
    A.Unit,
    A.Unitprice,
    A.Partialflag 
from tblPOdetails as A

Inner Join  ( SELECT  id, SUM(Qty) AS QtyDelivered
                                    FROM         dbo.tblPDdetails
                                    WHERE     (PONo = @PONumber)
                                    GROUP BY id)as B On A.id = B.id   
Inner Join tblpodetailshistory as C on A.id =C.id

where A.PONo = @PONumber)
END

其实不用写外层select，可以改写成

ALTER PROCEDURE [dbo].[POBalance]  @PONumber nvarchar(50)
AS BEGIN

Select 
    A.Description,
    C.qty as POqty,
    B.QtyDelivered as PDQty, 
    case when A.partialflag ='false' 
    then '0'
    else
    A.qty  end as Balance,
    A.Unit,
    A.Unitprice,
    A.Partialflag 
from tblPOdetails as A

Inner Join  ( SELECT  id, SUM(Qty) AS QtyDelivered
                                    FROM         dbo.tblPDdetails
                                    WHERE     (PONo = @PONumber)
                                    GROUP BY id)as B On A.id = B.id   
Inner Join tblpodetailshistory as C on A.id =C.id

where A.PONo = @PONumber
END

【讨论】：

它可以工作......真的不需要外部选择语句。

【参考方案2】：

问题出现在查询的开头，

Select( Select ....

删除最初的“Select (”并重试查询。当你运行一个

Select (Select ..) 

第二个选择只能返回一列（除非你连接返回的数据）。