How can I speed up and simplify query ?

I have rows in Tab1:

MyName, MyValue, ...
"AAA", 127, ...
"AAA", 127, ...
"AAA", 133, ...
"AAA", 127, ...
"BBB", 400, ...
"BBB", 400, ...

MyName + MyValue have duplicates :-(

I want to count distinct pairs MyName+MyValue This is my query:

    while
    select  MyName, MyValue
    from    Tab1
    group by MyName, MyValue
    where       ....
    {
        counter++;
    }
    //in this example counter = 3

Is it possible to speedup and simplify query ?