Eternal SELECT queries

[Aniceto Perez]

Hi

I have two tables: A and B. Table A has one field named CODI, char(5), and 4M records. Table B has two fields named COD1, char(2), and COD2, char(3), and 100K records. The CODI field has an index, also there is an index for both COD1 and COD2.

I am testing this query:

SELECT AVG(A.pre) FROM A INNER JOIN B ON A.CODI=B.COD1+B.COD2
WHERE B.F=2;

This query generates 100K registers and takes 180 secs with MS SQL Server.

This query with mySQL on the same machine has to be aborted after 3 hours of 100% CPU without any result record.

Does anybody know how to obtain results with "large" tables and queries with joins involving 2, 3 or 4 tables?

Thanks