Domain constraints in DBMS

A table is DBMS is a set of rows and columns that contain data. Columns in table have a unique name, often referred as attributes in DBMS. A domain is a unique set of values permitted for an attribute in a table. For example, a domain of month-of-year can accept January, February….December as possible values, a domain of integers can accept whole numbers that are negative, positive and zero.

Definition: Domain constraints are user defined data type and we can define them like this:
Domain Constraint = data type + Constraints (NOT NULL / UNIQUE / PRIMARY KEY / FOREIGN KEY / CHECK / DEFAULT)

Example:
For example I want to create a table “student_info” with “stu_id” field having value greater than 100, I can create a domain and table like this:

create domain id_value int
constraint id_test
check(value > 100);

create table student_info (
stu_id id_value PRIMARY KEY,
stu_name varchar(30),
stu_age int
);

Another example:
I want to create a table “bank_account” with “account_type” field having value either “checking” or “saving”:

create domain account_type char(12)
constraint acc_type_test
check(value in ("Checking", "Saving"));

create table bank_account (
account_nbr int PRIMARY KEY,
account_holder_name varchar(30),
account_type account_type
);