MYSQL query not using multiple column index
Posted on 2014-02-14
I have a multiple column index on a mysql table. Let's say the index is (first, second, third). When I run this query
SELECT first, second, third
EXPLAIN shows me it is using the index. But if I run the following query
SELECT first, second, third, fourth
it is not using the index.
Do I need all the columns that I am selecting to be in the index?