ER diagram to table mapping in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an ER diagram?

An ER diagram is a visual tool that shows entities (things), their attributes (details), and relationships (connections) between them in a database.

beginner

How do you map an entity from an ER diagram to a table?

Each entity becomes a table. The entity's attributes become columns in that table. The primary key attribute becomes the table's primary key.

intermediate

How are one-to-many relationships represented in tables?

Add a foreign key column in the table on the 'many' side. This foreign key points to the primary key of the 'one' side table.

intermediate

How do you map a many-to-many relationship from an ER diagram?

Create a new table called a junction or associative table. It contains foreign keys referencing the primary keys of the two related tables. These foreign keys together form the composite primary key.

advanced

What happens to weak entities in ER diagram to table mapping?

Weak entities become tables that include their own attributes plus a foreign key referencing the owner entity's primary key. The combination forms the weak entity's primary key.

In ER diagram to table mapping, what does an entity become?

A A table

B A column

C A foreign key

D A relationship

Each entity in an ER diagram is mapped to a table in the database.

How is a one-to-many relationship represented in tables?

A By adding a foreign key in the 'many' side table

B By merging both tables

C By creating a new table

D By adding a foreign key in the 'one' side table

The foreign key is placed in the table on the 'many' side pointing to the 'one' side.

What is used to represent a many-to-many relationship in tables?

A A foreign key in one table

B A new junction table

C A primary key in both tables

D No table needed

A new junction table with foreign keys to both related tables is created.

What forms the primary key of a weak entity table?

A Only its own attributes

B Only the foreign key from owner entity

C Combination of its own attributes and foreign key from owner entity

D No primary key

The primary key is a combination of the weak entity's attributes and the foreign key referencing the owner.

Which attribute becomes the primary key in the table mapped from an entity?

A Any attribute

B The first attribute listed

C The foreign key

D The attribute marked as primary key in ER diagram

The attribute identified as primary key in the ER diagram becomes the table's primary key.

Explain how to convert a many-to-many relationship from an ER diagram into tables.

Think about how to connect two tables that have many links to each other.

Describe the steps to map a weak entity from an ER diagram to a table.

Weak entities depend on another entity for identification.