This SQL tutorial explains how to use the SQL INTERSECT operator with syntax and examples.
The SQL 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.
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 SQL statement within the SQL INTERSECT must have the same number of fields in the result sets with similar data types.
The syntax for the SQL INTERSECT operator is:
SELECT expression1, expression2, ... expression_n FROM tables WHERE conditions INTERSECT SELECT expression1, expression2, ... expression_n FROM tables WHERE conditions;
The following is a SQL INTERSECT operator example that has one field with the same data type:
SELECT supplier_id FROM suppliers INTERSECT SELECT supplier_id FROM orders;
In this SQL 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 > 78 INTERSECT SELECT supplier_id FROM orders 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 suppliers table where the supplier_id is greater than 78 are returned. The second dataset has been filtered so that only records from the orders table are returned where the quantity is not equal to 0.
Next, let's look at an example of how to use the INTERSECT operator in SQL to return more than one column.
SELECT contact_id, last_name, first_name FROM contacts WHERE last_name <> 'Anderson' INTERSECT SELECT customer_id, last_name, first_name FROM customers WHERE customer_id < 50;
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 last_name is not Anderson. The records from the customers table are returned where the customer_id is less than 50.
The following is an INTERSECT example that uses a ORDER BY clause:
SELECT supplier_id, supplier_name FROM suppliers WHERE supplier_id > 2000 INTERSECT SELECT company_id, company_name FROM companies WHERE company_id > 1000 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.