SQL>
SQL> SELECT
2 TRIM('A' FROM 'ABCA') both,
3 TRIM(LEADING 'A' FROM 'ABCA') lead,
4 TRIM(TRAILING 'A' FROM 'ABCA') trail,
5 TRIM(' ABC ') blank
6 FROM dual;
BO LEA TRA BLA
-- --- --- ---
BC BCA ABC ABC
SQL>