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* How do you write this query?
@ 2002-10-31 18:21 Wei Weng <wweng@kencast.com>
2002-10-31 19:09 ` Re: How do you write this query? Richard Huxton <dev@archonet.com>
2002-11-01 07:51 ` Re: How do you write this query? Achilleus Mantzios <achill@matrix.gatewaynet.com>
0 siblings, 2 replies; 4+ messages in thread
From: Wei Weng @ 2002-10-31 18:21 UTC (permalink / raw)
To: pgsql-sql
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.
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: How do you write this query?
2002-10-31 18:21 How do you write this query? Wei Weng <wweng@kencast.com>
@ 2002-10-31 19:09 ` Richard Huxton <dev@archonet.com>
2002-10-31 20:38 ` Re: How do you write this query? Jean-Luc Lachance <jllachan@nsd.ca>
1 sibling, 1 reply; 4+ messages in thread
From: Richard Huxton @ 2002-10-31 19:09 UTC (permalink / raw)
To: Wei Weng <wweng@kencast.com>; pgsql-sql
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
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: How do you write this query?
2002-10-31 18:21 How do you write this query? Wei Weng <wweng@kencast.com>
2002-10-31 19:09 ` Re: How do you write this query? Richard Huxton <dev@archonet.com>
@ 2002-10-31 20:38 ` Jean-Luc Lachance <jllachan@nsd.ca>
0 siblings, 0 replies; 4+ messages in thread
From: Jean-Luc Lachance @ 2002-10-31 20:38 UTC (permalink / raw)
To: Richard Huxton <dev@archonet.com>; +Cc: Wei Weng <wweng@kencast.com>; pgsql-sql
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
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: How do you write this query?
2002-10-31 18:21 How do you write this query? Wei Weng <wweng@kencast.com>
@ 2002-11-01 07:51 ` Achilleus Mantzios <achill@matrix.gatewaynet.com>
1 sibling, 0 replies; 4+ messages in thread
From: Achilleus Mantzios @ 2002-11-01 07:51 UTC (permalink / raw)
To: Wei Weng <wweng@kencast.com>; +Cc: pgsql-sql
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.
>
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: if posting/reading through Usenet, please send an appropriate
> subscribe-nomail command to majordomo@postgresql.org so that your
> message can get through to the mailing list cleanly
>
==================================================================
Achilleus Mantzios
S/W Engineer
IT dept
Dynacom Tankers Mngmt
Nikis 4, Glyfada
Athens 16610
Greece
tel: +30-10-8981112
fax: +30-10-8981877
email: achill@matrix.gatewaynet.com
mantzios@softlab.ece.ntua.gr
^ permalink raw reply [nested|flat] 4+ messages in thread
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-- links below jump to the message on this page --
2002-10-31 18:21 How do you write this query? Wei Weng <wweng@kencast.com>
2002-10-31 19:09 ` Richard Huxton <dev@archonet.com>
2002-10-31 20:38 ` Jean-Luc Lachance <jllachan@nsd.ca>
2002-11-01 07:51 ` Achilleus Mantzios <achill@matrix.gatewaynet.com>
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