Hi All,
Example on optimizer
===============
postgres=# create table test(id int);
CREATE TABLE
postgres=# insert into test VALUES (1);
INSERT 0 1
postgres=# select * from test;
id
----
1
(1 row)
CREATE TABLE
postgres=# insert into test VALUES (1);
INSERT 0 1
postgres=# select * from test;
id
----
1
(1 row)
postgres=# explain select * from test;
QUERY PLAN
--------------------------------------------------------
Seq Scan on test (cost=0.00..34.00 rows=2400 width=4)
(1 row)
QUERY PLAN
--------------------------------------------------------
Seq Scan on test (cost=0.00..34.00 rows=2400 width=4)
(1 row)
In the above, example the optimizer is retreiving those many rows where there is only one row in that table. If i analyze am geting one row.
postgres=# ANALYZE test;
ANALYZE
postgres=# explain select * from test;
QUERY PLAN
----------------------------------------------------
Seq Scan on test (cost=0.00..1.01 rows=1 width=4)
(1 row)
ANALYZE
postgres=# explain select * from test;
QUERY PLAN
----------------------------------------------------
Seq Scan on test (cost=0.00..1.01 rows=1 width=4)
(1 row)
My question here is, what it retreiving as rows when there is no such. One more thing, if i wont do analyze and run the explain plan for three or more times, then catalogs getting updated automatically and resulting the correct row as 1.
Q2. Does explain , will update the catalogs automatically.
Regards
Raghavendra
