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MySQL Tutorial - Dividing Query Output into Groups

By: FYIcenter.com

(Continued from previous topic...)

How To Divide Query Output into Groups?

You can divide query output into multiple groups with the GROUP BY clause. It allows you specify a column as the grouping criteria, so that rows with the same value in that column will be considered as a single group. When the GROUP BY clause is specified, the select statement can only be used to return group level information. The following script gives you a good GROUP BY example:

mysql> SELECT tag, COUNT(*), MIN(created), AVG(counts) 
   FROM fyi_links GROUP BY tag;
| tag  | COUNT(*) | MIN(created)        | AVG(counts) |
| DBA  |        3 | 2005-01-01 00:00:00 |      3.6667 |
| DEV  |        2 | 2004-01-01 00:00:00 |      4.0000 |
| SQA  |        2 | 2003-01-01 00:00:00 |      7.0000 |
3 rows in set (0.07 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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