SQL GROUP BY

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What is SQL GROUP BY?

The SQL GROUP BY is a clause enables SQL aggregate functions for a grouping of information. For example, it could support subtotaling by region number in a sales table.

GROUP BY supports dividing data into sets so that aggregate functions like SUM, AVG and COUNT can be performed.

Why Use SQL GROUP BY?

The SQL GROUP BY clause is used whenever aggregate functions by group are required. This is an aid to understanding and analyzing information.

How To Use SQL GROUP BY

SQL GROUP BY is used as follows. It must follow the FROM and WHERE clauses. The columns in a SELECT clause must be either group by columns or aggregate function columns.

SQL GROUP BY Syntax

SELECT <column_name1>, <column_name2> <aggregate_function>
FROM <table_name>
GROUP BY <column_name1>, <column_name2>

SQL GROUP BY Example

The following example produces a count of branches by region_nbr from the branch table.

Here are the contents of the table:

Table: BRANCH

branch_nbr branch_name region_nbr employee_count

108 New York 100 10

110 Boston 100 6

212 Chicago 200 5

404 San Diego 400 6

415 San Jose 400 3

branch_nbr	branch_name	region_nbr	employee_count
108	New York	100	10
110	Boston	100	6
212	Chicago	200	5
404	San Diego	400	6
415	San Jose	400	3

This SQL Statement with GROUP BY is executed:

SELECT region_nbr, count(*)
FROM branch
GROUP BY region_nbr
ORDER BY region_nbr

Here is the result.

region_nbr count(*)

100 2

200 1

400 2

region_nbr	*count()**
100	2
200	1
400	2

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