Re: How do you write this query?

I have a table

Table "test"
Column | Type | Modifiers
--------+------------------------+----------
data | integer | not null
data1 | character varying(128) | not null
data2 | character varying(128) | not null

(Note: data is NOT the primary key.)

And
select * from test
returns

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

What do I do?

Thanks!

--
Wei Weng
Network Software Engineer
KenCast Inc.

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

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

On 31 Oct 2002, Wei Weng wrote:

and yet another equivalent query:

SELECT f1.data1 from test f1,test f2 where f1.data=3 and f1.data2 =
f2.data2 and f2.data1='pooh';

> I have a table
>
> Table "test"
> Column | Type | Modifiers
> --------+------------------------+----------
> data | integer | not null
> data1 | character varying(128) | not null
> data2 | character varying(128) | not null
>
> (Note: data is NOT the primary key.)
>
> And
> select * from test
> returns
>
>
> 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
>
>
> What do I do?
>
> Thanks!
>
> --
> Wei Weng
> Network Software Engineer
> KenCast Inc.
>
>
>
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> message can get through to the mailing list cleanly
>

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