Relational databases, SQL, & modeling

Question 1

What is a primary key?

Answer 1

Primary key - The identifier for each row (often id).

Question 2

What is a foreign key?

Answer 2

Foreign key - Data in one table that references a primary key in another table.

Question 3

What is a one-to-many relationship? Provide an example.

Answer 3

One row in Table A connects to many rows in Table B and one row in table B connects to one row in Table A.
Ex: One person owns several cars, but each car has one owner.

Question 4

What is a many-to-many relationship? Provide an example.

Answer 4

One row in Table A connects to many rows in Table B and one row in Table B connects to many rows in Table A.
Ex: One customer can purchase several products, each product can be purchased by several customers.

Question 5

What are the SQL queries?

Answer 5

INSERT INTO
SELECT FROM
UPDATE
DELETE FROM
WHERE

Question 6

How do you create a table using SQL queries?

Answer 6

CREATE TABLE ‘users-db’.’users’(
‘id’ INT NOT NULL AUTO_INCREMENT ,
‘username’ TEXT NOT NULL ,
‘email’ TEXT NOT NULL ,
PIMARY KEY (‘id’)
);

Question 7

How do you select the row with id 1?

Answer 7

SELECT *FROM users WHERE id = 1;

Question 8

How do you add new data using SQL queries?

Answer 8

Insert new row
INSERT INTO users (username, email)
VALUES (anna, anna.skog@mail.com);

Question 9

What is a relational database?

Answer 9

A relational database organizes data into rows and columns, which collectively form a table. Data is typically structured across multiple tables, which can be joined together via a primary key or a foreign key. These unique identifiers demonstrate the different relationships which exist between tables, and these relationships are usually illustrated through different types of data models.