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MySQL Tutorial - Using Multiple Columns in GROUP BY

By: FYIcenter.com

(Continued from previous topic...)

Can Multiple Columns Be Used in GROUP BY?

If you want to break your output into smaller groups, if you specify multiple column names or expressions in the GROUP BY clause. Output in each group must satisfy a specific combination of the expressions listed in the GROUP BY clause. The more columns or expressions entered in the GROUP BY clause, the smaller the groups will be.

The tutorial exercise below shows you how to break data into groups per "tag" and per year when they were created. Then the group function COUNT(*) is applied on each group:

mysql> SELECT tag, YEAR(created), COUNT(*) 
   FROM fyi_links GROUP BY tag, YEAR(created);
| tag  | YEAR(created) | COUNT(*) |
| DBA  |          2005 |        1 |
| DBA  |          2006 |        2 |
| DEV  |          2004 |        1 |
| DEV  |          2006 |        1 |
| SQA  |          2003 |        1 |
| SQA  |          2006 |        1 |
6 rows in set (0.00 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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