WITH t AS
(
SELECT 11 v1 FROM dual
UNION ALL SELECT 11 FROM dual
UNION ALL SELECT 11 FROM dual
UNION ALL SELECT 11 FROM dual
UNION ALL SELECT 11 FROM dual
UNION ALL SELECT 22 FROM dual
UNION ALL SELECT 22 FROM dual
UNION ALL SELECT 22 FROM dual
UNION ALL SELECT 22 FROM dual
UNION ALL SELECT 22 FROM dual
)
SELECT ROWNUM rn
     , v1
     , DECODE(v1, 11, 1, 22, 2) v2
     , CASE WHEN ROWNUM < 3 THEN NULL
            WHEN v1 = LAG(v1   ) OVER(ORDER BY ROWNUM)
             AND v1 = LAG(v1, 1) OVER(ORDER BY ROWNUM)
             AND v1 = LAG(v1, 2) OVER(ORDER BY ROWNUM)
            THEN 'T'
            ELSE 'F'
        END v3
  FROM t
;