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with t (col) as (
select '10573T2' from dual union all
select '3A1234F' from dual union all
select '23XXX02' from dual union all
select '4GABC23' from dual union all
select '31234FX' from dual
)
select *
from t
where REGEXP_LIKE(COL, '^[34][A-Za-z]')
| COL |
|---|
| 3A1234F |
| 4GABC23 |