Index doesn't work with < or >

[simplyroberto]

I've noticed that MYSQL is not using indexes when the operators "<" or ">" are used in the SELECT query; For example:

SELECT firstname
FROM users
WHERE birthyear < 1969

Now, birthyear is of type "int" and is indexed. However the EXPLAIN statement shows that all rows are examined!

Can anyone explain why?

Many thanks,
Roberto

 

[TonyGroves]

The MySQL optimiser has a mind of its own. Maybe in this case it has decided that it would be faster not to use an index.