The HAVING clause is used in SQL to specify conditions for groups in a query that have been grouped using the GROUP BY clause. The HAVING clause operates on the results of aggregate functions and is used to restrict the groups returned by a query based on a specified condition. The basic syntax of the HAVING clause is as follows:

SELECT column1, aggregate_function(column2), ..., aggregate_function(column_n)
FROM table_name
GROUP BY column1
HAVING condition;

In this syntax, condition is the condition that must be met for a group to be included in the results.

Let’s take a look at a few examples to understand the HAVING clause better:

Example 1:

SELECT city, SUM(population)
FROM cities
GROUP BY city
HAVING SUM(population) > 1000000;

In this example, the HAVING clause is used to restrict the groups returned by the query to only those cities with a total population greater than 1,000,000. The result of this query will be a table that displays the city name and the total population of each city that has a population greater than 1,000,000.

Example 2:

SELECT department, AVG(salary)
FROM employees
GROUP BY department
HAVING AVG(salary) > 50000;

In this example, the HAVING clause is used to restrict the groups returned by the query to only those departments with an average salary greater than $50,000. The result of this query will be a table that displays the department name and the average salary of each department that has an average salary greater than $50,000.

Example 3:

SELECT year, MONTH(order_date), SUM(total_sales)
FROM orders
GROUP BY year, MONTH(order_date)
HAVING SUM(total_sales) > 100000;

In this example, the HAVING clause is used to restrict the groups returned by the query to only those groups with total sales greater than $100,000. The result of this query will be a table that displays the year and month of the order, and the total sales for each group that has total sales greater than $100,000.

In conclusion, the HAVING clause is an important tool for filtering groups based on a specified condition in SQL. It allows you to restrict the groups returned by a query to only those groups that meet a specified condition, making it easier to analyze and understand the data.

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