SQL

Question 1

What is SQL?

Answer 1

Structured Query Language, used to communicate with the Database

Question 2

How is data organised in a relational database?

Answer 2

In tables

Question 3

What is a primary key?

Answer 3

It is a single field or combination of fields that defines the uniqueness of a row. A primary key cannot be null.

Question 4

What is a foreign key?

Answer 4

field which can uniquely identify each row in another table.

Question 5

What is a join?

Answer 5

A join defines the relationship betweem two tables. It links fields from each table that contain matching data.

Question 6

Image I had a table called table and I wanted to select all the data from it, what would the command be?

Answer 6

select * from table;

Question 7

Can you explain what a self join is and give an example?

Answer 7

A self join is a join which allows the table to join to itself. An example could be an employee table with managers. A manager is also an employee and you would therefore have to join to itself to get a relationship with an employee and manager.