子查询返回超过 1 个值。当子查询跟在 =,!=,<,<=,>,>= 之后或当子查询用作表达式时，这是不允许的答案

【问题标题】：Subquery returned more than 1 value.This is not permitted when the subquery follows =,!=,<,<=,>,>= or when the subquery is used as an expression子查询返回超过 1 个值。当子查询跟在 =,!=,<,<=,>,>= 之后或当子查询用作表达式时，这是不允许的
【发布时间】：2013-04-17 07:17:32
【问题描述】：

我有一个 select * from book table 的存储过程，使用子查询我的查询是

USE [library]
GO

/****** Object:  StoredProcedure [dbo].[report_r_and_l]    Script Date: 04/17/2013 12:42:39 ******/

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

ALTER procedure [dbo].[report_r_and_l]
@fdate date,
@tdate date,
@key varchar(1)
as

if(@key='r')

    select * 
    from dbo.books 
    where isbn =(select isbn from dbo.lending where (act between @fdate and @tdate) and (stat ='close'))

else if(@key='l')

    select * 
    from dbo.books 
    where isbn =(select isbn from dbo.lending where lended_date between @fdate and @tdate)

我知道子查询向主查询返回多个查询，但我不知道如何避免此错误，谁能帮助我？

【问题讨论】：

显然select isbn 返回的值不止一个。你可以使用where isbn IN (select isbn ...
使用select top 1 isbn ... 或select max(isbn) ...。即使你知道只会返回一行，sql-server 也不知道，因为错误信息是基于对命令的静态分析，而不是基于真实数据。

标签： sql-server subquery

【解决方案1】：

问题是这两个查询都返回了不止一行：

select isbn from dbo.lending where (act between @fdate and @tdate) and (stat ='close')
select isbn from dbo.lending where lended_date between @fdate and @tdate

您有两种选择，具体取决于您想要的结果。您可以将上述查询替换为保证返回单行的内容（例如，通过使用SELECT TOP 1），或者您可以将= 切换为IN 并返回多行，像这样：

select * from dbo.books where isbn IN (select isbn from dbo.lending where (act between @fdate and @tdate) and (stat ='close'))

【讨论】：

我得到了我的朋友，谢谢。我想知道一件事，只有一个在books表中引用选定的isbn，我想从借出表中选择isbn，从借出表中选择isbn sudent_name从学生表中引用借出表中的索引号，如何检索多个来自多个表的行？？
不，原始问题的架构有lended_date。无论您想变得多么迂腐，实际定义的架构每次都胜过良好的语法。
这真是我见过的对IN最简洁易懂的描述了，谢谢！

【解决方案2】：

使用In 而不是=

 select * from dbo.books
 where isbn in (select isbn from dbo.lending 
                where act between @fdate and @tdate
                and stat ='close'
               )

或者你可以使用Exists

SELECT t1.*,t2.*
FROM  books   t1 
WHERE  EXISTS ( SELECT * FROM dbo.lending t2 WHERE t1.isbn = t2.isbn and
                t2.act between @fdate and @tdate and t2.stat ='close' )

【讨论】：

SET atRate1 = (SELECT t1.*,t2.* FROM RateCode t1 WHERE EXISTS (SELECT * FROM RateAmount t2 WHERE t1.RateCode = t2.RateCode AND t1.CountryCode = @CCode AND t1.ModuleCode = @MCode)) 我在 t2 上遇到错误。*

【解决方案3】：

您可以使用 IN 运算符，如下所示

select * from dbo.books where isbn IN
(select isbn from dbo.lending where lended_date between @fdate and @tdate)

【讨论】：

【解决方案4】：

Using operator 'IN' helps

USE [library]
GO

/****** Object:  StoredProcedure [dbo].[report_r_and_l]    Script Date: 04/17/2013 12:42:39 ******/

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

ALTER procedure [dbo].[report_r_and_l]
@fdate date,
@tdate date,
@key varchar(1)
as

if(@key='r')

    select * 
    from dbo.books 
    where isbn IN (select isbn from dbo.lending where (act between @fdate and @tdate) and (stat ='close'))

else if(@key='l')

    select * 
    from dbo.books 
    where isbn IN (select isbn from dbo.lending where lended_date between @fdate and @tdate)

【讨论】：