Lesson 2: Joining Multiple Tables

Question 1

Primary key (PK)

Answer 1

The PRIMARY KEY is a column or columns that uniquely identifies each row in the table. It cannot be left NULL.

Question 2

Foreign key (FK)

Answer 2

The FOREIGN KEY is a key that is used to connect two tables. The FOREIGN KEY is a column or columns in one table that refers to the PRIMARY KEY column in another table.

Question 3

Joins

Answer 3

A join clause is used to combine rows from two or more tables, based on a related column between the tables.

Question 4

Left Join

Answer 4

The LEFT JOIN keyword returns all rows from the left table (we refer to this as table1), and the matching rows from the right table (we refer to this as table2). The result is a NULL from the right side, if there is no match.