One of the solutions:

sele accountno, balance from table1;
union;
sele accountno, balance from table2;
union;
sele accountno, balance from table3;
into curs temp1 nofilt

sele accountno, min(balance) from temp1 group by 1

>Hello Experts!
>
>I have three tables. Each of them I am storing date, accountno and balance for diferrent periods,e.g,in the the 1st table for 11th to last date of a month,in the second for 1st to 10th of the same month and in the third table for the previous month.Now I want to find the minimum balance for each account from the 3 tables. Please help me.