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Default

The DEFAULT constraint provides a default value for a column.

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

The following SQL sets a DEFAULT value for the "City" column when the "Persons" table is created:

My SQL / SQL Server / Oracle / MS Access:

CREATE TABLE Persons
(
City varchar(255) DEFAULT 'Sandnes'
);

The DEFAULT constraint can also be used to insert system values, by using functions like GETDATE():

CREATE TABLE Orders
(
OrderDate date DEFAULT GETDATE()
);

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

MySQL

ALTER TABLE Persons
ALTER City SET DEFAULT 'Sandnes';

SQL Server

ALTER TABLE Persons
ADD CONSTRAINT df_City
DEFAULT 'Sandnes' FOR City;

MS Access

ALTER TABLE Persons
ALTER COLUMN City SET DEFAULT 'Sandnes';

Oracle

ALTER TABLE Persons
MODIFY City DEFAULT 'Sandnes';

To drop a DEFAULT constraint, use the following SQL:

MySQL

ALTER TABLE Persons
ALTER City DROP DEFAULT;

SQL Server / Oracle / MS Access:

ALTER TABLE Persons
ALTER COLUMN City DROP DEFAULT;