DFF - Unable to default value the DFF based on SQL Query from the seeded field

We have created a DFF based on Grade.

The requirement is to populate the numeric digit of the Grade in the DFF Grade field.

For example:

When the Grade is updated to 7A, the DFF Grade should be updated to “7”. (Only the number should be visible)

We have tried the below two queries, but none of them worked:

(1)

SELECT SUBSTR(name,1,1)  FROM per_grades_f_vl pgfv  WHERE pgfv.grade_id = :{PARAMETER.GRADE_ID}    AND TRUNC(SYSDATE) BETWEEN pgfv.effective_start_date AND pgfv.effective_end_date

(2)

SELECT DISTINCT SUBSTR(pgfv.name,1,1) from per_all_people_f papf,per_all_assignments_f paam,PER_JOBS_F pjf,PER_JOB_FAMILY_F_TL pjfft,per_grades_f_vl pgfvWhere paam.grade_id = pgfv.grade_idAND papf.person_id = paam.person_id --Assignment dataand paam.primary_flag = 'Y'AND TRUNC(sysdate) BETWEEN papf.effective_start_date ANDpapf.effective_end_dateAND TRUNC(sysdate) BETWEEN paam.effective_start_date ANDpaam.effective_end_dateAND TRUNC(sysdate) BETWEEN pgfv.effective_start_date ANDpgfv.effective_end_dateAND paam.assignment_status_type = 'ACTIVE'and paam.person_id = nvl(to_number(:{PARAMETER.PERSON_ID}), paam.person_id)