SQL Having

In SQL, the HAVING clause is used in conjunction with the GROUP BY clause to filter the results of a query based on a condition applied to aggregated data. It is typically used when you want to filter the results based on the results of aggregate functions such as COUNT, SUM, AVG, etc.

Here’s the basic syntax of a query using HAVING:

sql

SELECT column1, column2, aggregate_function(column3)
FROM table
GROUP BY column1, column2
HAVING condition;

Let’s break down the components:

• SELECT: Specifies the columns you want to include in the result set.
• aggregate_function(column3): An aggregate function applied to column3, such as COUNT(column3), SUM(column3), etc.
• FROM: Specifies the table or tables from which to retrieve data.
• GROUP BY: Groups the result set by one or more columns (column1, column2 in the example).
• HAVING: Specifies the condition that must be met for a row to be included in the result set. This condition can include the results of aggregate functions.

Here’s an example to illustrate the usage of HAVING:

Suppose you have a table called orders with columns customer_id, order_date, and total_amount. You want to find customers who have made at least three orders and have spent a total amount greater than $100.

sql

SELECT customer_id, COUNT(*) as order_count, SUM(total_amount) as total_spent
FROM orders
GROUP BY customer_id
HAVING order_count >= 3 AND total_spent > 100;

In this example, the HAVING clause filters the result set to include only those rows where the order count (order_count) is greater than or equal to 3 and the total spent (total_spent) is greater than 100.