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SQL DEFAULT Constraint ❮ Previous Next ❯

SQL DEFAULT Constraint

The DEFAULT constraint is used to set 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:

My SQL / SQL Server / Oracle / MS Access:

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:

MySQL:

ALTER TABLE Persons ALTER City SET DEFAULT 'Sandnes';

SQL Server:

ALTER TABLE PersonsADD 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';

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; ❮ Previous Next ❯ ★ +1 Sign in to track progress

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