>>I realize that the original probably was ONLY example data. But the very first thought (guessing that NoProvince is intX typed) for optimization would be "Between" or the equivalent ">= and <=" query syntax to skip the problem Fabio mentioned ;-)
>
>Yes, we are talking about field of type integer.

So I am pretty certain that for contiuos ranges "Between" or the equivalent >= and <= in where clause should be faster, as only the range of the index needs to be checked, or to say it in Fabios words in this special case "and" can be used instead of "or"