MySQL ignores indexes if query contains conditions "greater than" or "smaller than"

[lpa]

Hello,

Does anyone know why MySQL is not using indexes in queries with conditions "greater than" or "is not empty":

select from table where col1='$col1' and col2 !='';

select from table where col1='$col1' and col2 > '0';

Indexes are used only if query contains condition "equal to":

select from table where col1='$col1' and col2 ='$col2';

Don't know how can I use indexes if I need to select columns where value is greater than something or value is not empty 🙁

[bradgrafelman]

What type of column is 'col2' ?

[lpa]

Both columns are INT.