SQL NOT NULL Constraint
By default, a column can hold NULL values.
The NOT NULL constraint enforces a column to NOT accept NULL values.
This enforces a field to always contain a value, which means that you cannot insert a new record, or update a r...See more
ecord without adding a value to this field.
SQL NOT NULL on CREATE TABLE
The following SQL ensures that the "ID", "LastName", and "FirstName" columns will NOT accept NULL values when the "Persons" table is created:
SQL NOT NULL on ALTER TABLE
To create a NOT NULL constraint on the "Age" column when the "Persons" table is already created, use the following SQL:
ALTER TABLE Persons
MODIFY Age int NOT NULL;
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