HAVING CLAUSE

 

This SQL tutorial explains how to use the SQL HAVING clause with syntax and examples.

DESCRIPTION

The SQL HAVING Clause is used in combination with the GROUP BY Clause to restrict the groups of returned rows to only those whose the condition is TRUE.

SYNTAX

The syntax for the SQL HAVING Clause is:

SELECT expression1, expression2, ... expression_n, 
       aggregate_function (aggregate_expression)
FROM tables
[WHERE conditions]
GROUP BY expression1, expression2, ... expression_n
HAVING condition;

Parameters or Arguments

expression1, expression2, ... expression_n

Expressions that are not encapsulated within an aggregate function and must be included in the GROUP BY Clause near the end of the SQL statement.

aggregate_function

This is an aggregate function such as the SUM, COUNT, MIN, MAX, or AVG functions.

aggregate_expression

This is the column or expression that the aggregate_function will be used on.

tables

The tables that you wish to retrieve records from. There must be at least one table listed in the FROM clause.

WHERE conditions

Optional. These are the conditions for the records to be selected.

HAVING condition

This is a further condition applied only to the aggregated results to restrict the groups of returned rows. Only those groups whose condition evaluates to TRUE will be included in the result set.

EXAMPLE - USING SUM FUNCTION

Let's look at a SQL HAVING clause example that uses the SQL SUM function.

You could also use the SQL SUM function to return the name of the department and the total sales (in the associated department). The SQL HAVING clause will filter the results so that only departments with sales greater than $1000 will be returned.

SELECT department, SUM(sales) AS "Total sales"
FROM order_details
GROUP BY department
HAVING SUM(sales) > 1000;

EXAMPLE - USING COUNT FUNCTION

Let's look at how we could use the HAVING clause with the SQL COUNT function.

You could use the SQL COUNT function to return the name of the department and the number of employees (in the associated department) that make over $25,000 / year. The SQL HAVING clause will filter the results so that only departments with more than 10 employees will be returned.

SELECT department, COUNT(*) AS "Number of employees"
FROM employees
WHERE salary > 25000
GROUP BY department
HAVING COUNT(*) > 10;

EXAMPLE - USING MIN FUNCTION

Let's next look at how we could use the HAVING clause with the SQL MIN function.

You could also use the SQL MIN function to return the name of each department and the minimum salary in the department. The SQL HAVING clause will return only those departments where the minimum salary is greater than $35,000.

SELECT department, MIN(salary) AS "Lowest salary"
FROM employees
GROUP BY department
HAVING MIN(salary) > 35000;

EXAMPLE - USING MAX FUNCTION

Finally, let's look at how we could use the HAVING clause with the SQL MAX function.

For example, you could also use the SQL MAX function to return the name of each department and the maximum salary in the department. The SQL HAVING clause will return only those departments whose maximum salary is less than $50,000.

SELECT department, MAX(salary) AS "Highest salary"
FROM employees
GROUP BY department
HAVING MAX(salary) < 50000;