How To Count Duplicated Values in a Column


How To Count Duplicated Values in a Column? - Oracle DBA FAQ - Understanding SQL SELECT Query Statements



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 employees table:

SQL> SELECT first_name, COUNT(*) FROM employees 
  GROUP BY first_name HAVING COUNT(*) > 1;
FIRST_NAME             COUNT(*)
-------------------- ----------
Peter                         3
Michael                       2
Steven                        2
John                          3
Julia                         2
William                       2
Karen                         2
Kevin                         2

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