SQL cascade deletion and cascade update

For more information about how to delete SQL cascading updates, see

For more information about how to delete SQL cascading updates, see

The Code is as follows:
On delete cascade

When you update or delete a primary key table, the foreign key table will be updated or deleted together. You need to set cascade attributes when creating the table.

Create table Countries (CountryId int primary key)
Insert into Countries (CountryId) VALUES (1)
Insert into Countries (CountryId) VALUES (2)
Insert into Countries (CountryId) VALUES (3)

Create table Cities (CityId int primary key, CountryId int references Countries on delete cascade );
Insert into Cities VALUES (1, 1)
Insert into Cities VALUES (2, 1)
Insert into Cities VALUES (3, 2)

Create table Buyers (CustomerId int primary key, CityId int references Cities on delete cascade );
Insert into Buyers VALUES (1, 1 ),
Insert into Buyers VALUES (2, 1)
Insert into Buyers VALUES (3, 2)

In addition, cascade updates
On update cascade