SQL DEFAULT Constraint

SQL DEFAULT Constraint

The DEFAULT constraint is used to insert a default value into a column.

The default value will be added to all new records, if no other value is specified.

SQL DEFAULT Constraint on CREATE TABLE

CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255) DEFAULT 'Sandnes'

SQL DEFAULT Constraint on ALTER TABLE
To create a DEFAULT constraint on the "City" column when the table is already created, use the following SQL:




ALTER TABLE Persons
ALTER COLUMN City SET DEFAULT 'SANDNES'
Oracle:


ALTER TABLE Persons
MODIFY City DEFAULT 'SANDNES'


To DROP a DEFAULT Constraint
To drop a DEFAULT constraint, use the following SQL:




ALTER TABLE Persons
ALTER COLUMN City DROP DEFAULT