In RDBMS, both the GROUP BY and HAVING clauses are used in combination with aggregate functions to perform operations on grouped data. However, they are used for different purposes in a query. 

In this blog post, we will go through the major difference between SQL Group BY and HAVING Clause. We will also look at some examples while going over the differences.

GROUP BY Clause:

The GROUP BY clause is used to group rows that have the same values in specified columns into summary rows, like a summary report. It is typically used with aggregate functions (e.g., SUM, AVG, COUNT) to perform calculations on each group of rows. The GROUP BY clause comes before the HAVING clause in a Structured Query Language(SQL) query.

Example of GROUP BY Clause

SELECT department, AVG (salary) as average_salary FROM employees GROUP BY department;

In this example, We are trying to find out the average salary from the employees table. Here, rows are grouped by the department column, and the average salary is calculated for each department.

HAVING CLAUSE

The HAVING clause is used to filter the results of a GROUP BY query based on a specified condition. It is similar to the WHERE clause but is specifically used with aggregate functions on grouped data. The HAVING clause comes after the GROUP BY clause in a SQL query.

Example of HAVING Clause

SELECT department, AVG (salary) as average_salary FROM employees GROUP BY department HAVING AVG(salary) > 75000;

In this example, the results are filtered from the employees table to include only those groups where the average salary is greater than 75000 USD.

In summary, GROUP BY clause is used to group rows based on specified columns and apply aggregate functions to those groups, while HAVING clause is used to filter the results of a GROUP BY query based on aggregate function conditions. When developers write the query, the order of these clauses in an SQL query is important: GROUP BY comes first, followed by HAVING.

Conclusion

In this blog post, we went through the major difference between GROUP BY and HAVING Clause in a database while going through examples.