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database/notes/02-integrity-er-diagram.md
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@ -3,6 +3,7 @@
![ERD](https://www.memecreator.org/static/images/memes/5074790.jpg) ![ERD](https://www.memecreator.org/static/images/memes/5074790.jpg)
## Agenda ## Agenda
* Database Schema
* Data Integrity * Data Integrity
* ER Diagrams * ER Diagrams
@ -75,9 +76,10 @@ INSERT INTO STUDENTS (id,name,age,phone,email,address,batch_id)
VALUES (3,"John Watson",30,123456789,"i.am@sherlock.ed","221B Baker Street", 3); VALUES (3,"John Watson",30,123456789,"i.am@sherlock.ed","221B Baker Street", 3);
``` ```
![Duplicate error](../media/duplicate-error.png) ![Duplicate error](../media/duplicate-error.png)
As you can see, the database does not allow us to insert a duplicate row. As you can see, the database does not allow us to insert a duplicate row.
![Gandalf](https://i.kym-cdn.com/entries/icons/original/000/002/144/You_Shall_Not_Pass!_0-1_screenshot.jpg) <img src="https://i.kym-cdn.com/entries/icons/original/000/002/144/You_Shall_Not_Pass!_0-1_screenshot.jpg" alt="Gandalf" width="300"/>
### Referential integrity ### Referential integrity
> Referential integrity is a property of data stating that all its references are valid. > Referential integrity is a property of data stating that all its references are valid.
@ -190,6 +192,7 @@ erDiagram
> A "one-to-one" relationship is seen when one instance of entity 1 is related to only one instance of entity 2 and vice-versa > A "one-to-one" relationship is seen when one instance of entity 1 is related to only one instance of entity 2 and vice-versa
A student can only have one email address and one email address can be associated with only one student. A student can only have one email address and one email address can be associated with only one student.
![One to One](../media/one-to-one.png) ![One to One](../media/one-to-one.png)
An attribute shared by both entities can be added to either of the entities. An attribute shared by both entities can be added to either of the entities.