EXPLAIN
SQL - Language Statements
EXPLAIN
Shows statement execution details
1998-09-01
EXPLAIN [ VERBOSE ] query
1998-09-01
Inputs
VERBOSE
Flag to show detailed query plan.
query
Any query.
1998-04-15
Outputs
NOTICE: QUERY PLAN:
plan
Explicit query plan from the Postgres backend.
EXPLAIN
Flag sent after query plan is shown.
1998-04-15
Description
This command outputs details about the supplied query.
The default output is the computed query cost.
The cost value is only meaningful to the optimizer in comparing
various query plans.
VERBOSE displays the full query plan and cost to your screen,
and pretty-prints the plan to the postmaster log file.
1998-04-15
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 rows=0 width=4)
EXPLAIN
Compatibility
1998-09-01
SQL92
There is no EXPLAIN statement defined in SQL92.