Du kan bruge følgende:
SQL> SELECT X, to_char(X, 'fm99999999.00000999')
2 FROM (SELECT 123 X FROM dual UNION ALL
3 SELECT 123.12 FROM dual UNION ALL
4 SELECT 123.123456 FROM dual);
X TO_CHAR(X,'FM99999999.00000999
---------- ------------------------------
123 123.00000
123.12 123.12000
123.123456 123.123456