>Madam
>
>In each table I shall store date,ano and balance for specific period and I shall find it from an another prg. Now I want to find the minimum balance of the accounts (one by one) among the three tables. Please inform me if I failed to clear it.

In other words, you want to find a minimum balance for a given account (or for every account) through history?

If yes, then Yuri's solution would work. You join all tables using union, then group by account number to find min.