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.
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.
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Improved By : Umesh Bhat