MySQL – GROUP BY Clause

You can use GROUP BY to group values from a column, and, if you wish, perform calculations on that column. You can use COUNT, SUM, AVG, etc., functions on the grouped column.

To understand GROUP BY clause, consider an employee_tbl table, which is having the following records −

mysql> SELECT * FROM employee_tbl;+------+------+------------+--------------------+|  id  | name | work_date  | daily_typing_pages |+------+------+------------+--------------------+|   1  | John | 2007-01-24 |        250         ||   2  | Ram  | 2007-05-27 |        220         ||   3  | Jack | 2007-05-06 |        170         ||   3  | Jack | 2007-04-06 |        100         ||   4  | Jill | 2007-04-06 |        220         ||   5  | Zara | 2007-06-06 |        300         ||   5  | Zara | 2007-02-06 |        350         |+------+------+------------+--------------------+7 rows in set (0.00 sec)

Now, suppose based on the above table we want to count number of days each employee did work.

If we will write a SQL query as follows, then we will get the following result −

mysql> SELECT COUNT(*) FROM employee_tbl;+---------------------------+|          COUNT(*)         |+---------------------------+|             7             |+---------------------------+

But this is not serving our purpose, we want to display total number of pages typed by each person separately. This is done by using aggregate functions in conjunction with a GROUP BY clause as follows −

mysql> SELECT name, COUNT(*)   -> FROM   employee_tbl    -> GROUP BY name;+------+----------+| name | COUNT(*) |+------+----------+| Jack |     2    || Jill |     1    || John |     1    || Ram  |     1    || Zara |     2    |+------+----------+5 rows in set (0.04 sec)

We will see more functionality related to GROUP BY in other functions like SUM, AVG, etc.

mysql-useful-functions.htm