SQL-where子句中的未知列

Question

我對SQL相當SQL ，我終生無法弄清為什么我不能在這里嘗試做些什么。 我正嘗試在旅行中獲得最少數量的免費座位，並按包裹ID進行分組。

子查詢中的第一個有效，但是第二個我無法確定。 它說

'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;

為什么這對第一個子查詢有效，但對第二個子查詢無效？

---

更新。當我在from子句中放入“子查詢”時，似乎出現了錯誤。 我不知道如何重寫有問題的查詢來解決此問題，我將非常感謝您的幫助。 謝謝..

Answer 1

我認為您不能在mysql和oracle的where子句中使用列別名

從mysql文檔

標准SQL不允許在WHERE子句中引用列別名。 之所以施加此限制，是因為在評估WHERE子句時，可能尚未確定列值。

您可以在GROUP BY，ORDER BY或HAVING子句中使用別名來引用該列：

我對sql server

補充：您的子查詢可能沒有得到Paket.PaketId 。 嘗試通過添加來修改大多數外部查詢的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;

同時從第一次select刪除別名，然后說select SuperPaket

Answer 2

您的列是Paket.PaketID而不是“ SuperPaket”，因此無論您在哪里使用superpaket，都應使用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;