Slow performance to use 'UNION'

[Blu]

Thanks for your help, I am not allowed to use the 'UNION ALL' since it will return the duplicate records.

INDEX_NAME                     TABLE_NAME                     COLUMN_NAME
------------------------------ ------------------------------ --------------------------
COMPANY_DEF_PERMS_PK           COMPANY_DEFAULT_PERMISSIONS    OBJECT_TYPE_ID
COMPANY_DEF_PERMS_PK           COMPANY_DEFAULT_PERMISSIONS    COMPANY_ID
CO_DEF_PERMISSIONS_IN1         COMPANY_DEFAULT_PERMISSIONS    COMPANY_ID
SUPPLIER_IN1                   SUPPLIER                       NAME
SUPPLIER_IN3                   SUPPLIER                       CONTACT_CONTACT_ID
SUPPLIER_IN4                   SUPPLIER                       COMPANY_ID
SUPPLIER_IN5                   SUPPLIER                       PARENT_SUPPLIER_ID
SUPPLIER_PK                    SUPPLIER                       SUPPLIER_ID
SUPPLIER_SPM_ACL_PK            SUPPLIER_SPM_ACL               SUPPLIER_SPM_ACL_ID
USERNAME_IN1                   USERNAME                       COMPANY_ID
USERNAME_IN2                   USERNAME                       CONTACT_CONTACT_ID

INDEX_NAME                     TABLE_NAME                     COLUMN_NAME
------------------------------ ------------------------------ --------------------------
USERNAME_IN3                   USERNAME                       USERTYPE_ID
USERNAME_IN4                   USERNAME                       SUPPLIER_ID
USERNAME_IN5                   USERNAME                       DROPTO_CONTACT_ID
USERNAME_IN6                   USERNAME                       REMITTO_CONTACT_ID
USERNAME_IN7                   USERNAME                       SHIPTO_CONTACT_ID
USERNAME_IN8                   USERNAME                       LAST_PROJECT_ID
USERNAME_IN9                   USERNAME                       USERNAME_ALIAS_ID
USERNAME_PK                    USERNAME                       USERNAME_ID
USERNAME_UK1                   USERNAME                       USERNAME
USERNAME_UK1                   USERNAME                       NAME_SPACE

Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=55 Card=17 Bytes=410
          )

   1    0   SORT (UNIQUE) (Cost=55 Card=17 Bytes=410)
   2    1     UNION-ALL
   3    2       FILTER
   4    3         NESTED LOOPS (Cost=22 Card=16 Bytes=384)
   5    4           NESTED LOOPS (Cost=3 Card=1 Bytes=16)
   6    5             TABLE ACCESS (BY INDEX ROWID) OF 'USERNAME'(Cost=2 Card=1 Bytes=8)
   7    6               INDEX (UNIQUE SCAN) OF 'USERNAME_PK' (UNIQUE)(Cost=1 Card=39444)
   8    5             TABLE ACCESS (BY INDEX ROWID) OF 'COMPANY_DEFAULT_PERMISSIONS' (Cost=1 Card=1 Bytes=8)
   9    8               INDEX (UNIQUE SCAN) OF 'COMPANY_DEF_PERMS_PK'(UNIQUE)
  10    4           TABLE ACCESS (FULL) OF 'SUPPLIER' (Cost=19 Card=16Bytes=128)
  11    3         FILTER
  12   11           TABLE ACCESS (FULL) OF 'SUPPLIER_SPM_ACL' (Cost=5
Card=1 Bytes=9)
  13   11           INDEX (UNIQUE SCAN) OF 'USERNAME_GROUP_MAP_PK' (UNIQUE) (Cost=1 Card=1 Bytes=8)
  14    2       HASH JOIN (Cost=27 Card=1 Bytes=26)
  15   14         TABLE ACCESS (FULL) OF 'SUPPLIER_SPM_ACL' (Cost=5 Card=28 Bytes=280)
  16   14         NESTED LOOPS (Cost=21 Card=328 Bytes=5248)
  17   16           TABLE ACCESS (BY INDEX ROWID) OF 'USERNAME' (Cost=2 Card=1 Bytes=8)
  18   17             INDEX (UNIQUE SCAN) OF 'USERNAME_PK' (UNIQUE) (Cost=1 Card=39444)
  19   16           TABLE ACCESS (FULL) OF 'SUPPLIER' (Cost=19 Card=328 Bytes=2624)