Subject: can i make this sql query more efficiant?
From: Robert Treat <xzilla@users.sourceforge.net>
To: pgsql-sql@postgresql.org
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Date: 03 Apr 2003 16:02:04 -0500
Message-Id: <1049403724.13799.5473.camel@camel>
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create table  baz (event text, level int);

insert into baz values ('x',1);
insert into baz values ('x',2);
insert into baz values ('x',3);
insert into baz values ('y',2);
insert into baz values ('y',3);
insert into baz values ('y',3);

select * from baz;

 event | level 
-------+-------
 x     |     1
 x     |     2
 x     |     3
 y     |     2
 y     |     3
 y     |     3
(6 rows)


I want to know how many ones, twos, and threes there are for each event:

select 
	event, 
	(select count(*) from baz a 
		where level = 1 and a.event=baz.event) as ones, 
	(select count(*) from baz a 
		where level = 2 and a.event=baz.event) as twos, 
	(select count(*) from baz a 
		where level = 3 and a.event=baz.event) as threes
from
	 baz
group by 
	event;

which gives me:

 event | ones | twos | threes 
-------+------+------+--------
 x     |    1 |    1 |      1
 y     |    0 |    1 |      2
(2 rows)


which is fine, but I am wondering if there is a better way to do this?
I'd mainly like to reduce the number of subqueries involved. Another
improvement would be to not have to explicitly query for each level,
though this isn't as big since I know the range of levels in advance
(famous last words for a dba :-) 

Thanks in advance,

Robert Treat