SELECT col1, col2, col3, col4
, COUNT(*) AS cnt
FROM yourTable
GROUP BY col1, col2, col3, col4
HAVING COUNT(*) > 1
Hvis der er flere kolonner, som du vil have vist, kan du JOIN ovenstående til tabellen:
SELECT t.*
, dup.cnt
FROM yourTable t
JOIN
( SELECT col1, col2, col3, col4
, COUNT(*) AS cnt
FROM yourTable
GROUP BY col1, col2, col3, col4
HAVING COUNT(*) > 1
) AS dup
ON t.col1 = dup.col1
AND t.col2 = dup.col2
AND t.col3 = dup.col3
AND t.col4 = dup.col4