Lecture 4

Question 1

What are SQL joins? and what are the 4 we must know?

Answer 1

A join clause is used to combine rows from two or more tables, based on a related column between them.
Inner, Outer, Left and Right

Question 2

Simple/INNER JOIN

Answer 2

Only the things that match on the left and the right.

SELECT *
FROM table1
INNER JOIN Table2
ON table1.KEY = Table2.KEY

Question 3

Left JOIN

Answer 3

Everything on the left, plus anything on the right that matches.

SELECT *
FROM table1
LEFT JOIN Table2
ON table1.KEY = Table2.KEY

Question 4

Right JOIN

Answer 4

Everything on the right, plus anything on the left that matches.

SELECT *
FROM table1
RIGHT JOIN Table2
ON table1.KEY = Table2.KEY

Question 5

Outer JOIN

Answer 5

Everything on the right, plus everything on the left.

SELECT *
FROM table1
OUTER JOIN Table2
ON table1.KEY = Table2.KEY

Question 6

AS

Answer 6

AS is an aliase to tables or columns to make queries shorter or more readable.

Question 7

USING

Answer 7

We can use USING if the names of columns in both join tables are equal.