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
The following SQL creates a DEFAULT constraint on the "City" column when the "Persons" table is created:
My SQL / SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255) DEFAULT 'Sandnes'
) |
The DEFAULT constraint can also be used to insert system values, by using functions like GETDATE():
CREATE TABLE Orders
(
O_Id int NOT NULL,
OrderNo int NOT NULL,
P_Id int,
OrderDate date DEFAULT GETDATE()
) |
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:
MySQL:
ALTER TABLE Persons
ALTER City SET DEFAULT 'SANDNES' |
SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ALTER COLUMN City SET DEFAULT 'SANDNES' |
To DROP a DEFAULT Constraint
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 |
 |
W3Schools' Online Certification Program
The perfect solution for professionals who need to balance work, family, and career building.
More than 4000 certificates already issued!
|
The HTML Certificate documents your knowledge of HTML, XHTML, and CSS.
The JavaScript Certificate documents your knowledge of JavaScript and HTML DOM.
The XML Certificate documents your knowledge of XML, XML DOM and XSLT.
The ASP Certificate documents your knowledge of ASP, SQL, and ADO.
The PHP Certificate documents your knowledge of PHP and SQL (MySQL).
| 
