MySQL find duplicate records

#1

SELECT offset, COUNT(offset)  

FROM log 

GROUP BY offset  

HAVING COUNT(offset) > 1;  

#2

SELECT A.id, A.ts, CONVERT(TIMEDIFF (B.ts,A.ts),CHAR) AS timedifference,a.offset,a.input_offset

FROM log A INNER JOIN log B ON B.id = (A.id + 1)

ORDER BY TIMEDIFF (B.ts,A.ts) DESC