Optimize many subqueries with same source - sql

Question

Does anyone have any idea how to optimize such a query?
How do you encapsulate this into one query?
,(SELECT top 1 WFD_AttDecimal2 as Nocleg
FROM WFElements INNER JOIN
WFElementDetails ON WFElements.WFD_ID = WFElementDetails.DET_WFDID
Where
WFD_STPID = #KrokSlownikUdostepnionyKraj
and dbo.ClearWFElemID (WFD_AttChoose20) = KrajDoDiety6 -- id kraju
and dbo.ClearWFElemID (WFD_AttChoose9) = #Spolka) as NoclegStawka7
,(SELECT top 1 WFD_AttDecimal3 as NoclegPrzelicznik
FROM WFElements INNER JOIN
WFElementDetails ON WFElements.WFD_ID = WFElementDetails.DET_WFDID
Where
WFD_STPID = #KrokSlownikUdostepnionyKraj
and dbo.ClearWFElemID (WFD_AttChoose20) = KrajDoDiety6 -- id kraju
and dbo.ClearWFElemID (WFD_AttChoose9) = #Spolka) as NoclegPrzelicznik7
,PelneDoby6 * (select MinDieta from #MinDieta where RodzajDelegacji = KrajZagr6) as MinIloscDiet7
from #Dieta4

Answer 1

You can use OUTER APPLY or CROSS APPLY and select all the necessary columns within that, you can then access all of them in the SELECT
SELECT
wfd.Nocleg as NoclegStawka7
, wfd.NoclegPrzelicznik as NoclegPrzelicznik7
, d.PelneDoby6 * (select md.MinDieta from #MinDieta md where RodzajDelegacji = KrajZagr6) as MinIloscDiet7
from #Dieta4 d
OUTER APPLY (
SELECT TOP (1)
WFD_AttDecimal2 as Nocleg,
WFD_AttDecimal3 as NoclegPrzelicznik
FROM WFElements INNER JOIN
WFElementDetails ON WFElements.WFD_ID = WFElementDetails.DET_WFDID
Where
WFD_STPID = #KrokSlownikUdostepnionyKraj
and dbo.ClearWFElemID (WFD_AttChoose20) = KrajDoDiety6 -- id kraju
and dbo.ClearWFElemID (WFD_AttChoose9) = #Spolka
) wfd;
Note also:
I suggest you rethink your usage of a scalar function ClearWFElemID as it can be slow. Use a join or a Table Valued function instead.
TOP (1) without an ORDER BY is a code-smell: you may get a different result each time.
Always specify the table alias when using subqueries, or you risk getting the wrong results.