Here is a simple implementation to perform ‘IF EXISTS’ check

PL/SQL:

DECLARE 

vCount NUMBER;

BEGIN

      SELECT COUNT(*)
        INTO vCount
        FROM TABLE_NAME
       WHERE COLUMN_NAME = 'YOUR_VALUE';

      IF vCount > 0 THEN
       /*  Exists */
       DBMS_OUTPUT.PUT_LINE('Exists');
       
      ELSE
      /*  Not exists */
       DBMS_OUTPUT.PUT_LINE('Does not exists');
       
      END IF;

END;