SELECT c.id,
     c.parent_id,
     c.name,
FROM Customer c
WHERE c.parent_id = '5'

SELECT c.id, c.parent_id, c.name,
  FROM Customer c
 WHERE c.parent_id = '5'
   AND c.id not in (5,6)

SELECT c.id, c.parent_id, c.name
  FROM ttest c
 WHERE c.parent_id in (5,6)
   AND c.id not in (5,6)


  ID  PARENT_ID NAME
---- ---------- ----------
   1          5 Cust 1
   2          5 Cust 2
   3          6 Cust 3
   4          6 Cust 4