Entity Relationship Diagrams define the connections between tables in database create an entity-relationship (ER) model

Entity Relationship Diagrams

An Entity Relationship Diagram (ERD) is a graphical illustration of how “entities” relate to each other within a system.  

ERDs for your project will need to show the relationships between your tables in your database.

Three types of an entity-relationship:

Diagram Name Description
One-to-One A Country has only one Capital, and a Capital is in only one Country.
One-to-Many A Biological Mother can have many children, and a child can have only Biological Mother.
Many-to-Many An Author can write several Books, and a Book can be written by several Authors

When linking between two tables, it is common for a field in the first table to link to the primary key of another table. In this case, the field in the first table will be called a foreign key.

Foreign key is a field in one table that is linked to the primary key in another table. 


The school holds competitions among Shanyrak/Teams. For each useful action, Shanirak points are scored. The deputy director keeps a record of all the items in the notebook. Counting and identifying all points takes a long time, and there may be errors. Automate the work.


Define entities for automated system and types of relationships between entities.




1. What is the usage of ERD?

2. How to draw ERD?

3. Explain what does "One-to-Many" mean?

4. Give examples of relationships "One-to-One", "One-to-Many", "Many-to-Many".

5. Name foreign keys on ERD

6. Questions on wikibooks


Ex. 1:

Ex. 2:

Exam questions:

Категория: Relational databases | Добавил: bzfar77 (03.11.2020)
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