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Oracle/PLSQL : HAVING Clause

Tutorial by:      Date: 2016-04-15 02:23:21

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

Description

The Oracle 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 HAVING clause in Oracle/PLSQL is:

SELECT expression1, expression2, ... expression_n,

       aggregate_function (aggregate_expression)

FROM tables

[WHERE conditions]

GROUP BY expression1, expression2, ... expression_n

HAVING having_condition;

Parameters or Arguments

expression1, expression2, ... expression_n

The expressions that are not encapsulated within an aggregate function and must be included in the GROUP BY clause.

aggregate_function

It can be a function such as SUM, COUNT, MIN, MAX, or AVG functions.

aggregate_expression

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

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 an Oracle HAVING clause example that uses the SUM function.

You could also use the SUM function to return the name of the department and the total sales (in the associated department). The Oracle HAVING clause will filter the results so that only departments with sales greater than $25,000 will be returned.

SELECT department, SUM(sales) AS "Total sales"

FROM order_details

GROUP BY department

HAVING SUM(sales) > 25000;

Example - Using COUNT function

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

You could use the COUNT function to return the name of the department and the number of employees (in the associated department) that make under $49,500 / year. The Oracle 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 < 49500

GROUP BY department

HAVING COUNT(*) > 10;

Example - Using MIN function

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

You could also use the MIN function to return the name of each department and the minimum salary in the department. The Oracle HAVING clause will return only those departments where the minimum salary is less than $42,000.

SELECT department, MIN(salary) AS "Lowest salary"

FROM employees

GROUP BY department

HAVING MIN(salary) < 42000;

Example - Using MAX function

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

For example, you could also use the MAX function to return the name of each department and the maximum salary in the department. The Oracle HAVING clause will return only those departments whose maximum salary is greater than $45,000.

SELECT department, MAX(salary) AS "Highest salary"

FROM employees

GROUP BY department

HAVING MAX(salary) > 45000;

 

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Oracle/PLSQL

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