Introduction
Dictionary database
Instruction
Incredible! Let's recap what we learned in this part.
You can join a table with itself. Each copy of the table must have an alias, and all column names must be prefixed with the corresponding table alias:
SELECT emp.name AS employee_name, supervisor.name AS supervisor_name FROM employee AS emp JOIN employee AS supervisor ON emp.supervisor_id = supervisor.id
As you may have guessed, you can combine self JOINs with other JOINs and SQL constructions.
Exercise
Select all data from the person table. It has five columns:
id– the ID of a given person,name– the name of a given person,mother_id– the ID of the person's mother,father_id– the ID of the person's father, andyear_born– a given person's year of birth.
Stuck? Here's a hint!
Type:
SELECT * FROM person
