Dimitry,

> > create a index on (fieldA, fieldB) seam to no help too much (it's
> speed only the work on FieldA, but not on fieldB)
>
> Drop this useless composite index and create two indexes one single
> fields. i.e. index on fieldA and another index on fieldB.

You don't have enough information to make such a broad statement!

It is possible that indexing either column is the wrong answer, and that a natural table scan would be the faster approach.

But to know the correct answer we need to ask questions, and not jump to conclusions.


Sean