From: | Johannes <jotpe(at)posteo(dot)de> |
---|---|
To: | "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
Subject: | Re: execute same query only one time? |
Date: | 2016-02-08 20:09:43 |
Message-ID: | 56B8F607.2090408@posteo.de |
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Lists: | pgsql-general |
Am 08.02.2016 um 20:15 schrieb David G. Johnston:
> On Mon, Feb 8, 2016 at 12:05 PM, Johannes <jotpe(at)posteo(dot)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?
Yes.
> What client are you using to execute these statements?
JDBC. I execute both statements at once and iterate through the resultsets.
Johannes
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