select qurery with diff tables

Hi;

please find the scenario

if the current region is DER means,we have to get the rows from

MAIN_TABLE_DER

if the current region is RET means,we have to get the rows from

MAIN_TABLE_RET

current region is not the column name( we are passing thru host variables) like :ws-cur-reg


select
inv_no,
inv_nme,
inv_loc

from tablename

Please help me