FOREIGN KEY

NOT NULL

UNIQUE

PRIMARY KEY

age

gender

id

contact_number

Guarantees uniqueness

Automatically generates primary keys

Prevents NULL insertion

Ensures sequential insertion only

SQL does not allow named constraints

Composite keys cannot be dropped

UNIQUE constraints are implemented as indexes

FOREIGN KEY constraints require indexes

MODIFY CONSTRAINT fk2

ADD CONSTRAINT fk2 FOREIGN KEY

DROP INDEX mm_constraint

DROP FOREIGN KEY fk2

Cascades update

Blocks update of referenced key

Prevents deletion

Sets foreign key to NULL

Modifying a column type

Adding NOT NULL constraint

Changing foreign key behavior

Dropping a column

Foreign key becomes NULL

Corresponding rows in mentorships are deleted

Update is restricted

Error is thrown

Transformation of multivalued attributes

Creating primary and candidate keys

Transformation of qualifications

Copying identifiers from the “one” side to the “many” side

Only optional attributes are preserved

Only PK tags are retained; FK tags removed

All associations must be preserved as separate tables

Every FK must reference a PK or CK of the associated class