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Evan
Feb 2nd, 2004, 04:31 PM
psql dbname
dbname=# EXPLAIN ANALYZE SELECT image_group,imageid, extention, description, username,TO_CHAR(date,'MM/DD/YYYY') as date FROM images WHERE image_group='3382';
Seq Scan on images (cost=0.00..2366.78 rows=510 width=108) (actual time=103.25..1041.29 rows=1 loops=1)
Total runtime: 1041.35 msec
Evan
Feb 2nd, 2004, 05:59 PM
EXPLAIN
Name
EXPLAIN — Shows statement execution details
EXPLAIN [ VERBOSE ] query
Inputs
VERBOSE
Flag to show detailed query plan.
query
Any query.
Outputs
NOTICE: QUERY PLAN: plan
Explicit query plan from the Postgres backend.
EXPLAIN
Flag sent after query plan is shown.
Description
This command outputs details about the supplied query. The default output is the computed query cost. VERBOSE displays the full query plan and cost to your screen, and pretty-prints the plan to the postmaster log file.
Notes
There is only sparse documentation on the optimizer's use of cost information in Postgres. General information on cost estimation for query optimization can be found in database textbooks. Refer to the Programmer's Guide in the chapters on indexes and the genetic query optimizer for more information.
Usage
To show a query plan for a simple query:
postgres=> explain select * from foo;
NOTICE: QUERY PLAN:
Seq Scan on foo (cost=0.00 size=0 width=4)
EXPLAIN
Compatibility
SQL92
There is no EXPLAIN statement defined in SQL92.
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