Select count(*)

Hi,

   I have two tables (A and B), with the same structure, but in different tablespaces. One (A) has 50 million records and was created by the other one (B) (by INSERT ... SELECT ....), with 100 million records. After the data load, the indexes were created and 'analyze compute' executed. Then, after I made some performance tests, the results seem very strange :

Test 1 :

set timing on;

select <columns>, ....
from A, B
where <indexed_column> = ....

Table B is faster, although it has the double of records. As more times this SQL is executed, the time of execution of both tables are almost the same.

Test 2 :

set timing on;

select count(*)
from A, B
where <indexed_column> = ....

Table A is faster.

Test 3 :

set timing on;

select count(*) from A, B

Table A is faster.

   Why table A is just faster when I run select count(*)? I´m using Oracle 8.0.6.0.0.

Thanks in advanced,
Carlos Received on Fri Jul 05 2002 - 13:11:54 CDT