If you have a column with duplicated values, and you want to know what are those duplicated values are and how many duplicates are there for each of those values, you can use the "GROUP BY ... HAVING" clause as shown in the following example. It returns how many duplicated first names in the ggl_team table:

SELECT first_name, COUNT(*) FROM ggl_team

GROUP BY first_name HAVING COUNT(*) > 1

GO

first_name count(*)

John 5

So we have "John" as duplicated first name 5 times in the ggl_team table.