SQL Database
SQL Null Not
SQL NOT NULL Constraint
A column may contain NULL values by default.
A column is required to NOT accept NULL values by the NOT NULL constraint.
Because of this, a field is required to have a value at all times. This implies that you cannot update or add a new record without first putting a value to the field.
SQL NOT NULL on CREATE TABLE
When the “Persons” table is created, the following SQL makes sure that the “ID,” “LastName,” and “FirstName” columns will not accept NULL values:
Example
-------- Example MUKAVU ------
SQL NOT NULL on ALTER TABLE
Use the following SQL to establish a NOT NULL constraint on the “Age” column when the “Persons” table has already been created:
SQL Server / MS Access:
ALTER TABLE Persons
ALTER COLUMN Age int NOT NULL;
My SQL / Oracle (prior version 10G):
ALTER TABLE Persons
MODIFY COLUMN Age int NOT NULL;
Oracle 10G and later:
ALTER TABLE Persons
MODIFY Age int NOT NULL;
