Will an index work on 2 out of 3 fields?

[aboyd]

Let's say I have a table with 10 fields. Let's say I create an index of field4 and field5. Then I issue this query:

SELECT * FROM table_name WHERE field4='foo' AND field5='bar' AND field6='baseball';

If I didn't mention field6, of course the index would be used. But does including field6 make MySQL ignore the index entirely?

-Anthony

[Lars_Berg]

check with the explain command.