>i try it as below it take between 1 to lesthan 2 Minutes? i think it must be faster

Just run it in the debugger and you'll see which lines are slow. Indexing 6M records should not be done there, as Tore said. If you don't have an index on F1 the locate can take a full table scan: slow as well. With both indexes in place and between(s, 0, 1000) it should not take more than a few secs. The seek in my code at least enforces the index on F1.

HTH

thomas