Need sql query to remove duplicates using UNION ALL clause

Question

Hi,
I have a sql query which has UNION clause.But the UNION clause is causing some performance issues.
To overcome that I have used UNION ALL to improve performance but its returning duplicates.
Kindly anyone send a sample SQL query where my primary objective is used to use UNION ALL clause and to consider unique rows (elimating duplicate
ones)
Any help will be needful for me
Thanks and Regards

Answer 1

why not UNION? :(
another way also use MINUS
SQL>
SQL> with t as
  2  (
  3  select 1 if from dual union all
  4  select 2 if from dual union all
  5  select 1 if from dual union all
  6  select 3 if from dual union all
  7  select 3 if from dual
  8  )
  9  ,t2 as
10  (
11  select 1 if from dual union all
12  select 2 if from dual union all
13  select 3 if from dual union all
14  select 4 if from dual union all
15  select 5 if from dual
16  )
17  (select if from t
18  union all
19  select if from t2)
20  /
        IF
         1
         2
         1
         3
         3
         1
         2
         3
         4
         5
10 rows selected
SQL> so
SQL>
SQL> with t as
  2  (
  3  select 1 if from dual union all
  4  select 2 if from dual union all
  5  select 1 if from dual union all
  6  select 3 if from dual union all
  7  select 3 if from dual
  8  )
  9  ,t2 as
10  (
11  select 1 if from dual union all
12  select 2 if from dual union all
13  select 3 if from dual union all
14  select 4 if from dual union all
15  select 5 if from dual
16  )
17  (select if from t
18  union all
19  select if from t2)
20  minus
21  select -99 from dual
22  /
        IF
         1
         2
         3
         4
         5
SQL>