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MySQL Tutorial - Counting Duplicated Values in a Column

By: FYIcenter.com

(Continued from previous topic...)

How To Count Duplicated Values in a Column?

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 fyi_team table:

mysql> SELECT first_name, COUNT(*) FROM fyi_team 
   GROUP BY first_name HAVING COUNT(*) > 1;
+------------+----------+
| first_name | COUNT(*) |
+------------+----------+
| John       |        6 |
+------------+----------+
1 row in set (0.01 sec)

(Continued on next topic...)

  1. What Is a SELECT Query Statement?
  2. How To Create a Testing Table with Test Data?
  3. How To Select All Columns of All Rows from a Table?
  4. How To Select Some Columns from a Table?
  5. How To Select Some Rows from a Table?
  6. How To Add More Data to the Testing Table?
  7. How To Sort the Query Output?
  8. Can the Query Output Be Sorted by Multiple Columns?
  9. How To Sort Output in Descending Order?
  10. How To Use SELECT Statement to Count Number of Rows?
  11. Can SELECT Statements Be Used on Views?
  12. How To Filter Out Duplications in Returning Rows?
  13. What Are Group Functions?
  14. How To Use Group Functions in the SELECT Clause?
  15. Can Group Functions Be Mixed with Non-group Selection Fields?
  16. How To Divide Query Output into Groups?
  17. How To Apply Filtering Criteria at Group Level?
  18. How To Count Duplicated Values in a Column?
  19. Can Multiple Columns Be Used in GROUP BY?
  20. Can Group Functions Be Used in the ORDER BY Clause?

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