Re: Subqueries or Joins? Problems with multiple table query

From: Stefan Schwarzer <stefan(dot)schwarzer(at)grid(dot)unep(dot)ch>
To: Thom Brown <thombrown(at)gmail(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Subqueries or Joins? Problems with multiple table query
Date: 2010-02-23 13:43:07
Message-ID: 747375FC-7552-46DF-8005-83313334D89E@grid.unep.ch
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>>> Select countries.name, basel.year, basel.value, cites.year,
>>> cites.value
>>> From countries
>>> Left Join basel on basel.id_country = countries.id_country and
>>> basel.value=1
>>> Left Join cites on cites.id_country = countries.id_country and
>>> cites.value=1
>>
>> I would have thought so, but the query turns forever.
>
> How many rows in each of your tables, and what indexes do you have?

around 5000 rows

> You may also wish to review Andreas' suggestions as they propose a
> more sensible table structure rather than having a table for each
> convention.

The table proposal really looks nice. But our database is structured
by variable - so each convention has its own table.

> You may also be interested in the tablefunc contrib module to help
> present your data in the format you require rather than having a join
> for each convention:

Yes, I use this for the online representation of the data. Very useful
indeed.

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