AT clauses can be used in FOR loops only.

       An AT TOP clause specifies that when a group starts, the
       statement in the AT TOP clause has to be executed before
       executing the main code in the FOR loop. An AT BOTTOM clause
       specifies that an action has to be executed after the last record
       of a group has been processed and before the first record in the
       next group.

       Format

         AT BOTTOM OF  field-name [,...] statement

         AT TOP OF  field-name [,...] statement