Hi, I wonder if a small enhancement to the mysql planner/optimizer could be made.
The current (mysql4.0) optimizer only uses one index per SELECT. Because of this some queries result in a slow fulltable scan even if all used columns are indexed. Example: SELECT * FROM table1 WHERE columnA='x' OR columnB='x' (Slow table scan even if columnA and columnB are indexd! Other Databases like PostgreSQL don't have this problem.) Since Mysql 4.0 a UNION can be used to speed this up. Example: SELECT * FROM table1 WHERE columnA='x' UNION SELECT * FROM table1 WHERE columnB='x' (Now we have two SELECT with one index each.) Couldn't the planner/optimizer be easely changed to do this UNION automaticly ? I think this would be a big improvement to mysql. If I port applications from other databases to mysql there are often queries like this. Either those queries run terrible slow an mysql or I have to manually convert them into UNIONs. Thanks in advance Gunnar -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
