PostgreSQL – GROUP BY

GROUP BY clause is used in a SELECT statement to group “like” records. You can specify one or more columns in the GROUP BY clause. It is used with aggregate functions – to obtain 1 value for a group of rows.

Syntax:

SELECT column1, agg_func(column2) FROM table_name GROUP BY column1;

Consider the employee table as shown below:

id	first_name	last_name	department	salary
101	bryan	walker	sales	50,000
102	alex	carpenter	accounts	55,000
103	sam	white	sales	60,000
104	john	barry	sales	54,000
105	bill	wood	accounts	65,000
106	robert	hopkins	support	70,000
107	david	lee	support	72,000
108	jack	sears	support	65,000
109	tom	young	sales	55,000

You can use GROUP BY clause to obtain maximum salary in each department as shown below:

SELECT department, max(salary) FROM employee GROUP BY department;

department    max
----------   ------
sales        60000
accounts     65000
support      72000

Get count of employees in each department as below:

SELECT department, count(id) FROM employee GROUP BY department;

department    count
----------   ------
sales        4
accounts     2
support      3