How EXISTScan be used in this scenario

Question

Hi All,
I want to use EXISTS in this query insted of IN.
Select <Column Name>
from <User>.<Table Name>@<Database link Name>
where <Column1 Name> in (1,2,3,4,5,6,7,18,20)
and <Column2 Name> in (1,2,3,4,5,6)
and <Column3 Name> <>'0000000000000000'
and <Column4 Name> >= (select Sysdate - <Column Name> from <Local Table Name>)
TIA.
Regards
Ayaz.

Answer 1

In this case you don't have a sub query. You can construct a subquery for the purposes of using EXISTS but I wouldn't recommend it. Curiously though, the example I used to check this out works quite well! However, it's the Range Scan versus the Full Scan on the index that's the important bit.
SQL> set autot on exp stat
SQL> SELECT empno FROM scott.emp WHERE empno IN(7369, 7499, 7521);
     EMPNO
      7369
      7499
      7521
Execution Plan
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=1 Card=3 Bytes=12)
   1    0   INLIST ITERATOR
   2    1     INDEX (RANGE SCAN) OF 'PK_EMP' (INDEX (UNIQUE)) (Cost=1 Card=3 Bytes=12)
Statistics
          0  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
        436  bytes sent via SQL*Net to client
        508  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          3  rows processed
SQL> 
SQL> SELECT empno FROM scott.emp e
  2  WHERE EXISTS(
  3    SELECT 7369 FROM dual WHERE e.empno = 7369
  4    UNION ALL
  5    SELECT 7499 FROM dual WHERE e.empno = 7499
  6    UNION ALL
  7    SELECT 7521 FROM dual WHERE e.empno = 7521
  8    );
     EMPNO
      7369
      7499
      7521
Execution Plan
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=43 Card=1 Bytes=4)
   1    0   INDEX (FULL SCAN) OF 'PK_EMP' (INDEX (UNIQUE)) (Cost=1 Card=14 Bytes=56)
   2    1     UNION-ALL
   3    2       FILTER
   4    3         FAST DUAL (Cost=2 Card=1)
   5    2       FILTER
   6    5         FAST DUAL (Cost=2 Card=1)
   7    2       FILTER
   8    7         FAST DUAL (Cost=2 Card=1)
Statistics
          0  recursive calls
          0  db block gets
          2  consistent gets
          0  physical reads
          0  redo size
        436  bytes sent via SQL*Net to client
        508  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          3  rows processed