Re: sql question regarding count(*)

i will think more abt this issue
and will discuss.


regds
mallah.

On Friday 07 March 2003 12:10 pm, Stephan Szabo wrote:
> On Fri, 7 Mar 2003, Rajesh Kumar Mallah wrote:
> > On Friday 07 March 2003 11:41 am, Stephan Szabo wrote:
> > > On Fri, 7 Mar 2003, Rajesh Kumar Mallah wrote:
> > > > Tomasz did you notice the two queries are totally differet on
> > > > different tables?
> > >
> > > A count() on a non-grouped table returns 1 row.
> > >
> > > A grouped table returns 1 row per group.  If there are no groups, no
> > > rows are returned.  If the groups are filtered by a having clause, it
> > > might also return no rows.
> >
> > True the second query does not return any row.
> > even in first case no rows are returned.
> >
> > where is the difference?
>
> I don't think I understand the question.
>
> select userid from users where userid=-1
> returns 1 row for each row the where clause returns true
> and 0 rows if there are none.
>
> select count(*) from users where userid=-1
> returns 1 row (it's not a grouped table)
>
> select count(*) from users where userid=-1 group by userid
> returns 1 row if there is at least 1 row having userid=-1
>  or 0 rows otherwise (either there is a group or there isn't)
>
> select count(*) from users where userid=-1 group by userid
>  having userid!=-1
> should return 0 rows because even if there is a group it'll fail the
> having clause.
>
>
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-- 

Regds
Mallah

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Rajesh Kumar Mallah,
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