Group By and Having clause in SQL

Understanding SQL GROUP BY Clause

Introduction to GROUP BY Clause

The SQL GROUP BY clause is used to group rows that have the same values in specified columns into summary rows.

Using GROUP BY

Let's consider a sample table called "Sales" to understand how GROUP BY works:

Product	Category	Amount
Product A	Electronics	1000
Product B	Clothing	500
Product C	Electronics	800
Product D	Books	300

Using GROUP BY with Aggregate Functions

You can combine GROUP BY with aggregate functions like SUM, AVG, COUNT, etc., to calculate summaries of grouped data:

SELECT Category, SUM(Amount) AS TotalSales
FROM Sales
GROUP BY Category;
    

Output:

Category	TotalSales
Electronics	1800
Clothing	500
Books	300

Using GROUP BY with HAVING Clause

The HAVING clause is used to filter results after grouping. It's similar to the WHERE clause but operates on grouped data:

SELECT Category, AVG(Amount) AS AvgAmount
FROM Sales
GROUP BY Category
HAVING AVG(Amount) > 750;
    

Output:

Category	AvgAmount
Electronics	900