tsql - Simple SQL Server queries taking forever when variables/functions are involved -


this i've been struggling while found way around it. have fact table in sql server dw has around 30m records, , integer field called datecreatedkey has non-clustered index on field. have function called dbo.fn_datekeyfromdate quite simply

declare @ret int = year(@date) * 10000 + month(@date) * 100 + day(@date)  return @ret

as see execution times below, if index doesn't work when using function or when using variable. not sure if i'm missing obvious?

now these execution times each of these 5 blocks of code:

  • a: 0.034s:

    select  *     #subs2    biwarehouse.dbo.factsubscriptions (nolock)    datecreatedkey >= 20170814

  • b: 15.4s:

    declare @fromdate int select  @fromdate = 20170814  select  *     #subs3    biwarehouse.dbo.factsubscriptions (nolock)    datecreatedkey >= @fromdate

  • c: 134s:

    select  *     #subs4    biwarehouse.dbo.factsubscriptions (nolock)    datecreatedkey >= dbo.fn_datekeyfromdate(getdate()-1)

  • d: 20s:

    declare @fromdate int select  @fromdate = dbo.fn_datekeyfromdate(getdate()-1)  select  *     #subs     biwarehouse.dbo.factsubscriptions (nolock)    datecreatedkey >= @fromdate

i indexes doesn't used when calling function, should work variable. compare execution plans sure.

try if want use function (maybe idea 130s example?):

declare @fromdate int select  @fromdate = dbo.fn_datekeyfromdate(getdate()-1)  select  *     #subs     biwarehouse.dbo.factsubscriptions (nolock)    datecreatedkey >= @fromdate

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