Cannot perform an aggregate function on an expression containing an aggregate or a subquery.

[Sal_64]

سلام
روی این خط

sum(case when  (select tarikh_check from sodor_check where sh_sanad=riz_pardakht.sh_sanad) 

 between @tarikh_f and @tarikh_v  then (mablagh_tarh+mablagh_tankhah) else 0  end)as pmg,

خطای فوق رخ میده ، چرا ؟

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