Re: How do you write this query?

Thank goodness for nested select!

select data1 from test where data2 = ( select distinct data2 from test
where data1 = 'pooh') and data = 3;

JLL

Richard Huxton wrote:
> 
> On Thursday 31 Oct 2002 6:21 pm, Wei Weng wrote:
> >  data | data1 | data2
> > ------+-------+-------
> >     1 | foo   | bar
> >     2 | greg  | bar
> >     3 | pooh  | bar
> >     4 | dah   | peng
> >
> > I need a query that returns me the "data1" that satisfies the logic of
> > the following pseudo code:
> >
> > 1: select data2 into @out from test where data1 = 'pooh'
> > 2: select data1 from test where data2 = @out and data = 3
> 
> The most literal would be something like:
> 
> SELECT t1.data1 FROM test t1
> WHERE t1.data=3 AND t1.data2 IN
>     (SELECT t2.data2
>     FROM test t2
>     WHERE t2.data1='pooh')
> 
> You can probably get away without the t1/t2 stuff but that should make things
> clear.
> 
> Since Postgresql isn't very good at optimising IN, you might want to rewrite
> it as an EXISTS query instead - see the manuals and mailing list archives for
> details.
> 
> HTH
> --
>   Richard Huxton
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 5: Have you checked our extensive FAQ?
> 
> http://www.postgresql.org/users-lounge/docs/faq.html