NULL Constraint

Allows a column to have a NULL value, representing the absence of data.

NULL Constraint Example

NOT NULL Constraint

Ensures that a column cannot have a NULL value, requiring data for every record.

NOT NULL Constraint Example

UNIQUE Constraint

Guarantees that all values in a column are distinct from one another.

UNIQUE Constraint Example

DEFAULT Constraint

Provides a predefined value for a column if no value is explicitly provided during insertion.

DEFAULT Constraint Example