SQL DEFAULT Constraint
SQL DEFAULT Constraint
The DEFAULT constraint is used to provide a default value for a column.
The default value will be added to all new records IF no other value is specified.
SQL DEFAULT on CREATE TABLE
The following SQL sets a DEFAULT value for the "City" column when the "Persons" table is created:
Syntax:
CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
City varchar(255) DEFAULT 'Sandnes'
);
The DEFAULT constraint can also be used to insert system values, by using functions like GETDATE():
CREATE TABLE Orders (
ID int NOT NULL,
OrderNumber int NOT NULL,
OrderDate date DEFAULT GETDATE()
);
SQL DEFAULT on ALTER TABLE
To create a DEFAULT constraint on the "City" column when the table is already created, use the following SQL:
Syntax:
ALTER TABLE Persons
ADD CONSTRAINT df_City
DEFAULT 'Sandnes' FOR City;
DROP a DEFAULT Constraint
To drop a DEFAULT constraint, use the following SQL:
Syntax:
ALTER TABLE Persons
ALTER COLUMN City DROP DEFAULT;
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