6. Union & Join

Union

Find a list of employee and branch names

SELECT employee.first_name AS Employee_Branch_Names
FROM employee
UNION
SELECT branch.branch_name
FROM branch;

Find a list of all clients & branch suppliers' names

SELECT client.client_name AS Non-Employee_Entities, client.branch_id AS Branch_ID
FROM client
UNION
SELECT branch_supplier.supplier_name, branch_supplier.branch_id
FROM branch_supplier;

Join

Add the extra branch

INSERT INTO branch VALUES(4, "Buffalo", NULL, NULL);

SELECT employee.emp_id, employee.first_name, branch.branch_name
FROM employee
JOIN branch    -- LEFT JOIN, RIGHT JOIN
ON employee.emp_id = branch.mgr_id;