Remember that once we create a FOREIGN KEY, the database will keep track of the connection between those two tables. This means that we won't be able to add a row with a foreign key value that doesn't exist in the other table.
We've created the tables employee and project for you. The table project now has the following definition:
CREATE TABLE project ( id integer PRIMARY KEY, name varchar(64), description text, manager_id integer, FOREIGN KEY (manager_id) REFERENCES employee(id) );
Try to run the template query, which inserts a row into the project table.
As you can see, the query failed – there's no one with id = 4 in the employee table.
