The HAVING clause in Oracle SQL

Topic Introduction: The HAVING clause in Oracle SQL is used to filter the results of a GROUP BY query. It allows you to apply conditions to groups of rows after they have been grouped using the GROUP BY clause. The HAVING clause is used to restrict the groups of rows that are returned based on the result of an aggregate function or a combination of aggregate functions. This is particularly useful when you want to filter the results of a grouped query based on some aggregate criteria.

The basic syntax for using the HAVING clause is as follows:

SELECT column1, column2, aggregate_function(column3)

FROM table_name

GROUP BY column1, column2

HAVING condition;

Here's an example to illustrate how to use the HAVING clause:

Suppose you have a table called employees that contains information about employees, including the total salary. You want to find the total employee salary for each department which department's total salary is greater than $10,000.

SELECT department_id, SUM(salary) as total_salary

FROM employees

GROUP BY department_id

HAVING SUM(salary) > 10000;

In this example:

We're selecting the department_id and calculating the sum of the salary for each department.

We use the GROUP BY clause to group the results by department_id.

The HAVING clause filters the grouped results, retaining only those where the sum of salary is greater than $10,000.

The HAVING clause allows you to filter the results based on aggregate functions such as SUM, COUNT, AVG, MAX, or MIN, making it a powerful tool for working with grouped data in SQL.