PostgreSQL - EXCEPT Keyword

The PostgreSQL EXCEPT keyword is used to compare the result-sets of two or more SELECT statements. It returns all records from the first result-set that do not appear in the second result-set.

While using EXCEPT 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 EXCEPT keyword in PostgreSQL is given below:

SELECT column1, column2, ... FROM table1
EXCEPT [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 EXCEPT keyword: To get the records of Name column which are not present in both record-sets, the following query can be used:

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

  
  

  This will produce the result as shown below:

  Name
  Mango

• Using EXCEPT keyword with WHERE clause: To fetch the records of Name column which are not present in both record-sets with the specified condition, the following query can be used:

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

  
  

  This will produce the following result:

  Name
  Mango
  Orange

• Using EXCEPT keyword with multiple columns: To fetch the records of Name and Brand columns which are not present in both record-sets, the following query can be used:

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

  
  

  This will produce the following result:

  Name	Brand
  Apple	Harvest
  Mango	LocalFarm
  Orange	Delicious
  Orange	Harvest