SQL | CREATE DOMAIN

Used in : Postgre sql
CREATE DOMAIN creates a new domain. A domain is essentially a data type with optional constraints (restrictions on the allowed set of values). The user who defines a domain becomes its owner.

Domains are useful for abstracting common constraints on fields into a single location for maintenance. For example, several tables might contain email address columns, all requiring the same CHECK constraint to verify the address syntax. Define a domain rather than setting up each table’s constraint individually.

Examples:

CREATE DOMAIN CPI_DATA AS REAL CHECK
(value >= 0 AND value <= 10);

Now CPI_DATA domain is create so, we can use this domain anywhere in any table of database as below :

CREATE TABLE student(
sid char(9) PRIMARY KEY,
name varchar(30),
cpi CPI_DATA
);

Every time cpi_data will check the constraint, when you add data in student table.

Example 1 :

Insert into student values (201501408,Raj,7.5); 
This will not violate the property of cpi. 

Example 2 :

Insert into student values (201501188,Dhaval,12); 
ERROR. This will violate the property of cpi.