How to count consecutive duplicates in a table?

Question

I have below question:
Want to find the consecutive duplicates

SLNO   NAME     PG   
1       A1      NO                   
2       A2      YES                    


        

Answer 1

Only requiring a single aggregation query and no joins (the rest of the calculation can be done with ROW_NUMBER, LAG and LAST_VALUE):

SELECT MAX( num_before_in_queue ) AS max_sequential_in_queue
FROM   (
  SELECT rn - LAST_VALUE( has_changed ) IGNORE NULL OVER ( ORDER BY ROWNUM ) + 1
           AS num_before_in_queue
  FROM   (
    SELECT pg,
           ROW_NUMBER() OVER ( ORDER BY slno ) AS rn,
           CASE pg WHEN LAG( pg ) OVER ( ORDER BY slno )
                   THEN NULL
                   ELSE ROW_NUMBER() OVER ( ORDER BY sl_no )
                   END AS change
    FROM   table_name
  )
  WHERE  pg = 'Y'
);