PostgreSQL - INTERSECT Keyword

The PostgreSQL INTERSECT keyword is used to return the intersection of result-set of two or more SELECT statements. If a record exists in both result-sets, it will be included in the INTERSECT results. However, if a record exists in one result-set and not in the other, it will be removed from the INTERSECT results.

While using INTERSECT keyword, the following criteria must be satisfied:

• Number of columns in each SELECT statement should equal.
• Datatype of columns in each SELECT statement should match.
• Order of columns in each SELECT statement should match.

Syntax

The syntax for using INTERSECT keyword in PostgreSQL is given below:

SELECT column1, column2, ... FROM table1
INTERSECT [ALL]
SELECT column1, column2, ... FROM table2

Example:

Consider database tables called Product and Inventory with the following records:

Table 1: Product table

Table 2: Inventory table

• Using INTERSECT keyword: To get the records of Name column which are present in both record-sets, the following query can be used:

  SELECT Name FROM Product
  INTERSECT
  SELECT Name FROM Inventory
  ORDER BY Name;
  

  
  

  This will produce the result as shown below:

  Name
  Apple
  Orange
  Watermelon

• Using INTERSECT keyword with WHERE clause: To fetch the records of Name column which are present in both record-sets with the specified condition, the following statement can be used:

  SELECT Name FROM Product
  INTERSECT
  SELECT Name FROM Inventory
  WHERE Quantity < 30
  ORDER BY Name;
  

  
  

  This will produce the following result:

  Name
  Apple
  Watermelon

• Using INTERSECT keyword with multiple columns: To fetch the records of Name and Brand columns which are present in both record-sets, the query will be:

  SELECT Name, Brand FROM Product
  INTERSECT
  SELECT Name, Brand FROM Inventory
  ORDER BY Name;
  

  
  

  This will produce the following result:

  Name	Brand
  Apple	Delicious
  Watermelon	LocalFarm