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SQL Query Processing

  • November 14, 2008 at 1:04 pm

    #193799

    Is this the correct way that a query is processed?

    from

    where

    group by

    having

    select

    order by

    into

    If this is correct, what is the explanation of a query like

    select col1,count(*)

    from #table

    where date>=getdate()

    group by col1

    having count(*)>2

    if the having is processed before the select - how does it know how the count(*) is being aggregated?

  • November 14, 2008 at 1:36 pm

    #898865

    The having clause is evaluated after the group by clause. A group by is required to use a having. It is unassociated with the select portion of the statement. You don't have to select count(*) to use having count(*) > x. The having is essentially a where clause on the grouping, and the select is returning what you want to the screen. One does not rely on the other.

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