Message-Id: <5.1.1.6.0.20021118124632.01b5dcf0@wolf.csuohio.edu>
Date: Mon, 18 Nov 2002 12:55:33 -0500
To: pgsql-sql@postgresql.org
From: Ellen Cyran <ellen@urban.csuohio.edu>
Subject: slow group by query
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Is there any way to make this query faster?  I have indexes on year, 
msa_code, and sic.  I've also tried it with
an index on the combined group by columns.  I've made both sort_mem and 
shared_buffers bigger, but still this query
takes 40 seconds when I select 4 msa_codes and 7 minutes when I select 40 
msa_codes.  Would it just be better
to transpose the table to begin with and avoid the group by all together?

SELECT b.msa_code, b.sic, b.own, b.ind_div,
  (select emp from tbl_bls_msa as bls
where bls.year = '1975' and bls.msa_code = b.msa_code and bls.sic = b.sic 
and bls.own = b.own and bls.ind_div = b.ind_div ) AS emp1975,
  (select emp from tbl_bls_msa as bls
where bls.year = '1976' and bls.msa_code = b.msa_code and  bls.sic = b.sic 
and bls.own = b.own and bls.ind_div = b.ind_div ) AS emp1976,
  (select emp from tbl_bls_msa as bls
where bls.year = '1977' and bls.msa_code = b.msa_code  and  bls.sic = b.sic 
and bls.own = b.own and bls.ind_div = b.ind_div ) AS emp1977,
(select emp from tbl_bls_msa as bls
where bls.year = '1978' and bls.msa_code = b.msa_code and  bls.sic = b.sic 
and bls.own = b.own and bls.ind_div = b.ind_div ) AS emp1978,
(select emp from tbl_bls_msa as bls
where bls.year = '1990' and bls.msa_code = b.msa_code  and  bls.sic = b.sic 
and bls.own = b.own and bls.ind_div = b.ind_div)  AS emp1990
  FROM tbl_bls_msa AS b
where msa_code in ('1680','1640','0040','0120','0080')
GROUP BY b.msa_code, b.sic, b.ind_div, b.own ;

NOTICE:  QUERY PLAN:

Group  (cost=635.97..695.18 rows=592 width=22)
   ->  Sort  (cost=635.97..635.97 rows=5921 width=22)
         ->  Index Scan using msa_code_tbl_bls_msa_key, 
msa_code_tbl_bls_msa_key,
  msa_code_tbl_bls_msa_key, msa_code_tbl_bls_msa_key, 
msa_code_tbl_bls_msa_key on
  tbl_bls_msa b  (cost=0.00..264.99 rows=5921 width=22)
   SubPlan
     ->  Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa 
bls  (cost=0.00
..53.71 rows=1 width=10)
     ->  Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa 
bls  (cost=0.00
..53.71 rows=1 width=10)
     ->  Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa 
bls  (cost=0.00
..53.71 rows=1 width=10)
     ->  Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa 
bls  (cost=0.00
..53.71 rows=1 width=10)
     ->  Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa 
bls  (cost=0.00
..53.71 rows=1 width=10)

Thanks.
Ellen
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