Resolution:
EXEC SQL Select a into :HV1 where col_a IN (:group-var)
01 GROUP-VAR.
05 ELEM-VAR1 PIC X.
05 ELEM-VAR2 PIC X.
01 ELGROUP-VAR PIC X(2) redefines GROUP-VAR.
Then code the EXEC SQL statement to use the elementary definition. For the above example, use this:
EXEC SQL Select a into :HV1 where col_a = :elgroup-var
Instead of this:
EXEC SQL Select a into :HV1 where col_a = :group-var