Between table and table set up the primary key, foreign key relationships, have what use? What is the difference between with inner join?

CodePudding user response:

Have no relationship, both the main foreign key can be inner join,
Set the main foreign key, can realize cascade operation, removed the main table data, for example, the table's primary key is a foreign key in other tables data also can delete together,
In the practical application of less real set this cascade relationship