Question

我试图将如下所示的外部查询中的列传递给WHERE子句中的内部查询，而MySQL不喜欢它。我不确定如何重写此查询以使其工作。

我收到的错误消息是 where子句中的未知列'y.DateShipped'

我要执行的操作是使用小于DateShipped的EffectiveDate联接到内部表中的行，并且也是内部联接中的最大EffectiveDate（对于同一组，可以有多个行，通过不同的有效日期）

我很想知道如何使它起作用或重写它以便起作用。我正在使用MySQL 5.6，因此我没有可用的窗口函数，否则我认为这可以工作。

select 
    x.id,
    y.id,
    y.DateShipped 
from Shipment y inner join
    (select id, SourceId, DestinationId, SourcePPFContractId, EffectiveDate 
    from Relationship where EffectiveDate <= y.DateShipped order by 
    EffectiveDate desc limit 1) x 
on x.DestinationId = y.DestinationCustomerId 
and x.SourceId = y.OriginCustomerId 
and x.SourcePPFContractId = y.OriginContractId;

Answer 1

首先执行内部选择（来自“关系”），然后与第一次选择合并。这就是为什么它不起作用。您应该将DateShipped移到第一个选择项的where子句中：

select 
    x.id,
    y.id,
    y.DateShipped 
from Shipment y inner join
    (select id, SourceId, DestinationId, SourcePPFContractId, EffectiveDate 
    from Relationship order by 
    EffectiveDate desc limit 1) x 
on x.DestinationId = y.DestinationCustomerId 
and x.SourceId = y.OriginCustomerId 
and x.SourcePPFContractId = y.OriginContractId
and x.EffectiveDate <= y.DateShipped;

Answer 2

您需要在子查询中列出发货表才能正确调用它：

select 
    x.id,
    y.id,
    y.DateShipped 
from Shipment y inner join
    (select id, SourceId, DestinationId, SourcePPFContractId, EffectiveDate 
    from Relationship, Shipment where EffectiveDate <= Shipment.DateShipped order by 
    EffectiveDate desc limit 1) x 
on x.DestinationId = y.DestinationCustomerId 
and x.SourceId = y.OriginCustomerId 
and x.SourcePPFContractId = y.OriginContractId;

Answer 3

您正在尝试一种称为横向联接的方法-MySQL不支持这种方法。因为只需要一列，所以可以使用相关的子查询：

select (select r.id 
        from Relationship r
        where r.DestinationId = s.DestinationCustomerId and
              r.SourceId = s.OriginCustomerId and
              r.SourcePPFContractId = s.OriginContractId and
              r.EffectiveDate <= s.DateShipped
        order by r.EffectiveDate desc
        limit 1
       ) as x_id,
       s.id, s.DateShipped 
from Shipment s ;

请注意，我还将表别名更改为表名的缩写-这样查询就更易于阅读。

MYSQL：错误代码：1054。“ where子句”中的未知列

3 个答案: