#INNER JOIN: Intersection between 2 tables
SELECT *
FROM A
INNER JOIN B ON A.key = B.key
#LEFT JOIN: left table with the intersection joined to the right table
SELECT *
FROM A
LEFT JOIN B ON A.key = B.key
#LEFT JOIN(without intesection): left table without the intersection joined
# to the right table
SELECT *
FROM A
LEFT JOIN B ON A.key = B.key
WHERE B.key IS NULL
#RIGHT JOIN: right table with the intersection joined to the left table
SELECT *
FROM A
RIGHT JOIN B ON A.key = B.key
#RIGHT JOIN(without intesection): right table without the intersection joined
# to the left table
SELECT *
FROM A
RIGHT JOIN B ON A.key = B.key
WHERE A.key IS NULL # there seems to be a mistake on the site (B changed to A)
#FULL JOIN: union of 2 table
SELECT *
FROM A
FULL JOIN B ON A.key = B.key
#FULL JOIN(without intesection): union of two table without the intersection
SELECT *
FROM A
FULL JOIN B ON A.key = B.key
WHERE A.key IS NULL
OR B.key IS NULL