Oracle / PLSQL: INTERSECT Operator

This Oracle tutorial explains how to use the Oracle INTERSECT operator with syntax and examples.

Description

The Oracle INTERSECT operator is used to return the results of 2 or more SELECT statements. However, it only returns the rows selected by all queries or data sets. If a record exists in one query and not in the other, it will be omitted from the INTERSECT results.

Intersect Query

Explanation: The INTERSECT query will return the records in the blue shaded area. These are the records that exist in both Dataset1 and Dataset2.

Each SELECT statement within the INTERSECT must have the same number of fields in the result sets with similar data types.

Syntax

The syntax for the INTERSECT operator in Oracle/PLSQL is:

SELECT expression1, expression2, ... expression_n
FROM tables
[WHERE conditions]
INTERSECT
SELECT expression1, expression2, ... expression_n
FROM tables
[WHERE conditions];

Parameters or Arguments

expression1, expression2, ... expression_n

The columns or calculations that you wish to retrieve.

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. The conditions that must be met for the records to be selected.

Note

• There must be same number of expressions in both SELECT statements and have similar data types.

Example - With Single Expression

The following is an Oracle INTERSECT example that returns one field with the same data type:

SELECT supplier_id
FROM suppliers
INTERSECT
SELECT supplier_id
FROM orders;

In this INTERSECT example, if a supplier_id appeared in both the suppliers and orders table, it would appear in your result set.

Now, let's complicate our example further by adding WHERE conditions to the INTERSECT query.

SELECT supplier_id
FROM suppliers
WHERE supplier_id <= 99
INTERSECT
SELECT supplier_id
FROM orders
WHERE quantity > 25;

In this example, the WHERE clauses have been added to each of the datasets. The first dataset has been filtered so that only records from the suppliers table where the supplier_id is less than or equal to 99 are returned. The second dataset has been filtered so that only records from the orders table are returned where the quantity is greater than 25.

Example - With Multiple Expressions

Next, let's look at an example of how to use the INTERSECT operator in Oracle to return more than one column.

For example:

SELECT contact_id, last_name, first_name
FROM contacts
WHERE first_name <> 'John'
INTERSECT
SELECT customer_id, last_name, first_name
FROM customers
WHERE customer_id >= 89;

In this INTERSECT example, the query will return the records from the contacts table where the contact_id, last_name, and first_name values match the customer_id, last_name, and first_name value from the customers table.

There are WHERE conditions on each data set to further filter the results so that only records from the contacts are returned where the first_name is not John. The records from the customers table are returned where the customer_id is greater than or equal to 89.

Example - Using ORDER BY

The following is an INTERSECT example that uses an ORDER BY clause:

SELECT supplier_id, supplier_name
FROM suppliers
WHERE supplier_id > 500
INTERSECT
SELECT company_id, company_name
FROM companies
WHERE company_name in ( 'Apple', 'GCP', 'Oracle' )
ORDER BY 2;

Since the column names are different between the two SELECT statements, it is more advantageous to reference the columns in the ORDER BY clause by their position in the result set. In this example, we've sorted the results by supplier_name / company_name in ascending order, as denoted by the ORDER BY 2.

The supplier_name / company_name fields are in position #2 in the result set.