Re: execute same query only one time?

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От David G. Johnston
Тема Re: execute same query only one time?
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Msg-id CAKFQuwa47Kn5jTP_QxVOhmigsP9OAs0-HmO4ogDixgGCRRZ0+A@mail.gmail.com
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Ответ на execute same query only one time?  (Johannes <jotpe@posteo.de>)
Ответы Re: execute same query only one time?  (Johannes <jotpe@posteo.de>)
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On Mon, Feb 8, 2016 at 12:05 PM, Johannes <jotpe@posteo.de> wrote:
Hi,

is there a best practice to share data between two select statements?

Imaging following situation: I want to receive two result sets from two
tables, referring to a specific id from table t0 AND I try not to query
for that specific id a second time.

Table t0 returns 1 row and table t1 returns multiple rows.

begin;
select id, col1, col2, ... from t0 where id = (select max(id) from t0
where col1 = value1 and col2 = value2 and ...);
select col1 from t1 where t0_id = (select max(id) from t0 where col1 =
value1 and col2 = value2 and ...);
commit;

Please confirm:​

​You want the​ result of "SELECT max(id) FROM t0" to be used in the second query without having to recompute it?

What client are you using to execute these statements?

Dave

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