SQL Server: INTERSECT Operator

In this post explains how to use the INTERSECT operator in SQL Server (Transact-SQL) with syntax and examples.

Description

The SQL Server (Transact-SQL) INTERSECT operator is used to return the records that are in common between two SELECT statements or data sets. If a record exists in one query and not in the other, it will be omitted from the INTERSECT results. It is the intersection of the two SELECT statements.

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 SQL Server INTERSECT must have the same number of columns in the result sets with similar data types.

Syntax

The syntax for the INTERSECT operator in SQL Server (Transact-SQL) is:

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

Parameters or Arguments

expressions

The columns or calculations that you wish to compare between the two SELECT statements. They do not have to be the same fields in each of the SELECT statements, but the corresponding columns must be similar data types.

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.
• The corresponding columns in each of the SELECT statements must have similar data types.
• The INTERSECT operator returns only records in common between the SELECT statements.

Example - With Single Expression

Let's look at an example of an INTERSECT query in SQL Server (Transact-SQL) that returns one column with the same data type.

For example:

SELECT product_id
FROM products
INTERSECT
SELECT product_id
FROM inventory;

In this INTERSECT example, if a product_id appeared in both the products and inventory tables, it would appear in your result set for this INTERSECT query.

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

SELECT product_id
FROM products
WHERE product_id >= 50
INTERSECT
SELECT product_id
FROM inventory
WHERE quantity > 0;

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 products table where the product_id is greater than or equal to 50 are returned. The second dataset has been filtered so that only records from the inventory table are returned where the quantity is greater than 0.

Example - With Multiple Expressions

Next, let's look at an example of an INTERSECT query in SQL Server (Transact-SQL) that returns more than one column.

For example:

SELECT contact_id, last_name, first_name
FROM contacts
WHERE last_name = 'Mark'
INTERSECT
SELECT employee_id, last_name, first_name
FROM employees;

In this INTERSECT example, the query will return the intersection of the two SELECT statements. So if there are records in the contacts table with a contact_id, last_name, and first_name value that matches the employee_id, last_name, and first_name value in the employees table, the INTERSECT query will return these records. If there is no match, then the INTERSECT will not return the record.

Example - Using ORDER BY

Finally, let's look at how to use the ORDER BY clause in an INTERSECT query in SQL Server (Transact-SQL).

For example:

SELECT supplier_id, supplier_name
FROM suppliers
WHERE supplier_id > 500
INTERSECT
SELECT company_id, company_name
FROM companies
WHERE company_name in ( 'Apple', 'Microsoft', 'SQL Server' )
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.