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

SELECT MAX(consecutives) -- Block 1
FROM (
    SELECT t1.pg, t1.slno, COUNT(*) AS consecutives -- Block 2
    FROM test t1 INNER JOIN test t2 ON t1.pg = t2.pg
    WHERE t1.slno <= t2.slno
      AND NOT EXISTS (
        SELECT *  -- Block 3
        FROM test t3 
        WHERE t3.slno > t1.slno
          AND t3.slno < t2.slno
          AND t3.pg  != t1.pg
    )    
    GROUP BY t1.pg, t1.slno
);

The query calculates the result in following way:

• Extract all couples of records that don't have a record with different value of PG in between (blocks 2 and 3)
• Group them by PG value and starting SLNO value -> this counts the consecutive values for any [PG, (starting) SLNO] couple (block 2);
• Extract Maximum value from query 2 (block 1)

Note that the query may be simplified if the slno field in table contains consecutive values, but this seems not your case (in your example record with SLNO = 5 is missing)