SQL-where子句中的未知列

Question

我对SQL相当SQL ，我终生无法弄清为什么我不能在这里尝试做些什么。 我正尝试在旅行中获得最少数量的免费座位，并按包裹ID进行分组。

子查询中的第一个有效，但是第二个我无法确定。 它说

'where子句'中未知的列SuperPaket 。

select Paket.PaketID as "SuperPaket", Beskrivning, Resa.AvgångStad, Resa.AvgångTid, Resa.AvgångDatum,

    (select AnkomstTid from Resa where Resa.ResID in 
        (select ResID from PaketResa where PaketResa.PaketID = SuperPaket and Ordningsnr =
            (select max(Ordningsnr) from PaketResa where PaketResa.PaketID = SuperPaket))) "AnkomstTid",

        (select min(LedigaPlatser) from
            (select sum(AntalPlatser - Count) "LedigaPlatser", ResID from(
                select Bokning.ResID, AntalPlatser, sum(Bokning.AntalBiljetter) as Count from 
                    (Resa inner join Bokning on Resa.ResID = Bokning.ResID) where Bokning.ResID in
                        (select PaketResa.ResID from PaketResa where PaketResa.PaketID = SuperPaket)
                group by Bokning.ResID order by Count desc)
            as CountTable group by ResID) 
        as T) "LedigaPlatser"

    from ((Paket inner join PaketResa on Paket.PaketID = PaketResa.PaketID) inner join Resa on PaketResa.ResID = Resa.ResID) group by Paket.PaketID;

为什么这对第一个子查询有效，但对第二个子查询无效？

---

更新。当我在from子句中放入“子查询”时，似乎出现了错误。 我不知道如何重写有问题的查询来解决此问题，我将非常感谢您的帮助。 谢谢..

Answer 1

我认为您不能在mysql和oracle的where子句中使用列别名

从mysql文档

标准SQL不允许在WHERE子句中引用列别名。 之所以施加此限制，是因为在评估WHERE子句时，可能尚未确定列值。

您可以在GROUP BY，ORDER BY或HAVING子句中使用别名来引用该列：

我对sql server

补充：您的子查询可能没有得到Paket.PaketId 。 尝试通过添加来修改大多数外部查询的from子句

(select Paket.PaketID as "SuperPaket" from Paket)

如下

from (
      (Paket inner join PaketResa on Paket.PaketID = PaketResa.PaketID)   
inner join Resa on PaketResa.ResID = Resa.ResID),
      (select Paket.PaketID as "SuperPaket" from Paket)
group by Paket.PaketID;

同时从第一次select删除别名，然后说select SuperPaket

Answer 2

您的列是Paket.PaketID而不是“ SuperPaket”，因此无论您在哪里使用superpaket，都应使用Paket.PaketID

select Paket.PaketID as "SuperPaket", Beskrivning, Resa.AvgångStad, 
        Resa.AvgångTid, Resa.AvgångDatum,

(select AnkomstTid from Resa where Resa.ResID in 
    (select ResID from PaketResa where PaketResa.PaketID = Paket.PaketID and Ordningsnr =
        (select max(Ordningsnr) from PaketResa where PaketResa.PaketID = Paket.PaketID))) "AnkomstTid",

    (select min(LedigaPlatser) from
        (select sum(AntalPlatser - Count) "LedigaPlatser", ResID from(
            select Bokning.ResID, AntalPlatser, sum(Bokning.AntalBiljetter) as Count from 
                (Resa inner join Bokning on Resa.ResID = Bokning.ResID) where Bokning.ResID in
                    (select PaketResa.ResID from PaketResa where PaketResa.PaketID = Paket.PaketID)
            group by Bokning.ResID order by Count desc)
        as CountTable group by ResID) 
    as T) "LedigaPlatser"

from ((Paket inner join PaketResa on Paket.PaketID = PaketResa.PaketID) inner join Resa on PaketResa.ResID = Resa.ResID) group by Paket.PaketID;