Warum hat diese Abfrage zwei Auswahlmöglichkeiten?

Question

Ich habe diese Anfrage:

SELECT   WorkId, RegisterDate, sum(RoomType1) As RoomType1, sum(RoomType2) As RoomType2, sum(RoomType3) As RoomType3, sum(RoomType4) As RoomType4, sum(RoomType5) As RoomType5, sum(RoomType6) As RoomType6, sum(RoomType7) As RoomType7, sum(RoomType8) As RoomType8 
FROM (

SELECT  dbo.[Work].WorkId, dbo.[Work].RegisterDate, 

case dbo.Floor.RoomType when 1 then 1 else 0 end as RoomType1, 
     case dbo.Kat.RoomType when 2 then 1 else 0 end as RoomType2, 


FROM   dbo.Belediye INNER JOIN 
         dbo.[Is] ON dbo.Municipality.MunicipalityId= dbo.[Is].MunicipalityWorkId INNER JOIN 
         dbo.Look ON dbo.[Work].LookWorkId = dbo.Look.LookId , 
WHERE  (dbo.Look.LocationIS NOT NULL) 

) E 
GROUP BY WorkId, 

Diese Abfrage funktioniert wie erwartet, aber ich kann nicht verstehen, warum es zwei wählt hat, warum es sie braucht? Bitte erklären Sie es mir. Vielen Dank.

Answer 1

Wie Sie diese Abfrage Verdacht nicht brauchen zwei wählt und konnte ohne Unter Abfrage neu geschrieben werden:

SELECT i.IsId, 
     i.KayitTarihi, 
     SUM(case k.OdaTipi when 1 then 1 else 0 end) as RoomType1, 
     SUM(case k.OdaTipi when 2 then 1 else 0 end) as RoomType2, 
     SUM(case k.OdaTipi when 3 then 1 else 0 end) as RoomType3, 
     SUM(case k.OdaTipi when 4 then 1 else 0 end) as RoomType4, 
     SUM(case k.OdaTipi when 5 then 1 else 0 end) as RoomType5, 
     SUM(case k.OdaTipi when 6 then 1 else 0 end) as RoomType6, 
     SUM(case k.OdaTipi when 7 then 1 else 0 end) as RoomType7, 
     SUM(case k.OdaTipi when 8 then 1 else 0 end) as RoomType8 
FROM dbo.Belediye b 
INNER JOIN dbo.[Is] i 
    ON b.BelediyeId = i.BelediyeIsId 
INNER JOIN dbo.YerGorme yg 
    ON i.YerGormeIsId = yg.YerGormeId 
INNER JOIN dbo.Kat k 
    ON yg.YerGormeId = k.YerGorme_YerGormeId 
WHERE yg.Lokasyon IS NOT NULL 
GROUP BY i.IsId, i.KayitTarihi 

Anmerkung: Mit table aliases