MySQL multicolumn index
Should I include `col3` & `col4` in my index on `MyTable` if this is the only query I intend to run on my database? 

    Select MyTable.col3, MyTable.col4
    From MyTable 
    Inner Join MyOtherTable
    On MyTable.col1 = MyOtherTable.col1
    And MyTable.col2 = MyOtherTable.col2;
    

The tables I'm using have about half a million rows in them.  For the purposes of my question, `col1` & `col2` are a unique set found in both tables.

Here's the example table definition if you really need to know:

    CREATE TABLE MyTable 
    (col1 varchar(10), col2 varchar(10), col3 varchar(10), col4 varchar(10));
    
    CREATE TABLE MyOtherTable 
    (col1 varchar(10), col2 varchar(10));

So, should it be this?
 

       CREATE MyIdx ON MyTable (col1,col2);

Or this?
 

       CREATE MyIdx ON MyTable (col1,col2,col3,col4);
MySQL multicolumn index
===

Should I include `col3` & `col4` in my index on `MyTable` if this is the only query I intend to run on my database? 

    Select MyTable.col3, MyTable.col4
    From MyTable 
    Inner Join MyOtherTable
    On MyTable.col1 = MyOtherTable.col1
    And MyTable.col2 = MyOtherTable.col2;
    

The tables I'm using have about half a million rows in them.  For the purposes of my question, `col1` & `col2` are a unique set found in both tables.

Here's the example table definition if you really need to know:

    CREATE TABLE MyTable 
    (col1 varchar(10), col2 varchar(10), col3 varchar(10), col4 varchar(10));
    
    CREATE TABLE MyOtherTable 
    (col1 varchar(10), col2 varchar(10));

So, should it be this?
 

       CREATE MyIdx ON MyTable (col1,col2);

Or this?
 

       CREATE MyIdx ON MyTable (col1,col2,col3,col4);