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Message-ID: <7104a7370510260816l9262d19j808d23c023e8445e@mail.gmail.com>
Date: Wed, 26 Oct 2005 18:16:13 +0300
From: Volkan YAZICI <volkan.yazici@gmail.com>
To: pgsql-sql@postgresql.org
Subject: Combining two SELECTs by same filters
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Hi,

I've a table like:

=3D> SELECT dt FROM sales WHERE id =3D 2;
           dt
----------------------------
 2005-10-25 21:43:35.870049
 2005-10-25 21:43:36.254122
 2005-10-25 21:43:36.591196
 2005-10-25 21:43:36.893331
 2005-10-25 21:43:37.265671
 2005-10-25 21:43:37.688186
 2005-10-25 22:25:35.213171
 2005-10-25 22:25:36.32235
(8 rows)

And I want to collect the count of sales at hour =3D 21 and hour =3D 22.
For this purpose, I'm using below SELECT query:

=3D> SELECT
->     (SELECT count(id) FROM sales
->         WHERE id =3D 2
->         AND date_trunc('hour', dt) =3D '2005-10-25 21:00:00'),
->     (SELECT count(id) FROM sales
->         WHERE id =3D 2
->         AND date_trunc('hour', dt) =3D '2005-10-25 22:00:00');
 ?column? | ?column?
----------+----------
        6 |        2
(1 row)

Isn't it possible to combine these two SELECTs as one. Because one of
their filters are same: id =3D 2. I'm just trying to avoid making 2
scans with nearly same filters.

Regards.