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The SQL Group By statement is used to organize similar data into groups. The data is further organized using an equivalent function. It means that if multiple rows in a specific column have the same values, they will be grouped.

The SELECT statement is combined with the GROUP BY clause in a SQL query:

• The WHERE clause comes before the GROUP BY clause in SQL.
• The ORDER BY clause comes after the GROUP BY clause in SQL.

Syntax:

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE condition
GROUP BY column_name;

Note: GROUP BY clause is typically used with aggregate functions like SUM, COUNT, AVG, MIN, or MAX to compute summary information for each group.

Example:

Consider an Employee table:

EmpId	FirstName	LastName	Salary	DeptId
1	John	King	33000	1
2	James	Bond	33000	1
3	Neena	Patel	17000	2
4	Lex	De Haan	15000	1
5	Amit	Patel	15000	1
6	Abdul	Kalam	25000	2

• Query to count the number of employees in each department:

SELECT DeptId, COUNT(EmpId) as 'Number of Employees' 
FROM Employee
GROUP BY DeptId;

The ‘No of Employees’ column is an abbreviation for the COUNT(EmpId) column. The query returns the following result.

Output:

DeptId	No of Employees
1	4
2	2

• GROUP BY with WHERE clause:

SELECT EmpId, Salary 
FROM Employee 
WHERE LastName = "Patel"
GROUP BY Salary

The above query is used to select EmpId and Salary with WHERE clause and Group BY clause being on the SALARY column.

Output:

EmpId	Salary
3	17000
5	15000

Note: also read about SQL: ORDER BY Clause

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