On DELETE cascade and on UPDATE cascade

This is an optional database foreign key definition that sets the transformation rules for the response field in the Foreign key table when the data of the referenced column in the primary key table changes. Update is the value of the referenced field in the primary key table, and delete refers to the deletion of a record in the primary key table:
On update and on Delete can be followed by four words
No action, set NULL, set default, Cascade
No action means no action,
Set NULL indicates that the corresponding field in the foreign-key table has a null
Set default means setting to defaults
Cascade represents cascading operations, that is, if the primary key table is updated in the Reference field, the Foreign key table is also updated, the records in the primary key table are deleted, and the row in the Foreign key table is deleted accordingly

On DELETE cascade and on UPDATE cascade