Re: index(column1,column2)

[Thomas CORBIERE]

Hello,

This syntax allows you to create a covering index.
It is usefull if you are using both columns in a WHERE clause :

SELECT * FROM t WHERE column1=10 AND column2=5

An extra feature is that with the following index : INDEX(c1,c2,c3)
MySQL acts as if there was three indexes :
- INDEX(c1)
- INDEX(c1,c2)
- INDEX(c1,c2,c3)

That is you can use the leftmost columns in your seach condition.

Regards,

Thomas CORBIERE