SQL

Question 1

In the LEFT JOIN below which table returns all row?

Which table fills matching rows and returns null for non-matching rows?

SELECT *
FROM newspaper
LEFT JOIN online
ON newspaper.id = online.id;

Answer 1

The newspaper table returns ALL rows.

The online table FILLS matching rows and returns NULL for non-matching rows.

Question 2

What is a primary key calls that appears in another table?

Answer 2

Foreign Key

Question 3

What is the primary and foreign key in this example, and are they the same value?

SELECT *
FROM classes
JOIN students
ON classes.id = students.class_id;

Answer 3

Yes, they are the same value.

Primary key is classes.id
Foreign key is students.class_id