SQL cascade deletion and Cascade update _mssql

Copy Code code as follows:

ON DELETE Cascade

When you update or delete a primary key table, the foreign key table is also updated or deleted, and the cascading properties need to be set when the table is being built

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, cascading updates
ON UPDATE cascade