1) SELECT * FROM table WHERE col1='A'

2) SELECT * FROM table WHERE col1='A' OR col1='B'

Considering that we have an index on col1, does anyone know why the index is used inthe first statement but not the second?

it shouldn't do although that may depend on the DB server and version

how do you know that it does?

Sorry that i wasn't clear!!!

We are using MySql 4.1 and i know by using EXPLAIN.

Also, if you take a look at and look at http://dev.mysql.com/doc/refman/5.0/...l-indexes.html and read the post Posted by [name withheld] on June 4 2003 2:21am, the poster says, 'The 'not using indexes when using OR' feature is rather annoying'

Thanks for your help and guidance.