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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.
PostgreSQL EXCEPT

Syntax

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

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

Note: By default, EXCEPT clause only takes distinct values. To select duplicate values, EXCEPT ALL clause can be used.

Example:

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

Table 1: Product table

NameBrandPriceQuantity
AppleDelicious1.540
AppleHarvest1.650
OrangeDelicious2.040
OrangeHarvest1.950
WatermelonLocalFarm4.050
MangoLocalFarm3.560

Table 2: Inventory table

NameBrandPriceQuantity
AppleDelicious1.520
OrangeLocalFarm2.040
WatermelonLocalFarm4.020

  • 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:

    NameBrand
    AppleHarvest
    MangoLocalFarm
    OrangeDelicious
    OrangeHarvest

❮ PostgreSQL Keywords