ER Diagrams

ER Diagrams are a visual representation of the database structure.

Related:

• Why use ER diagrams
• Mermaid

Example

Entities are tables in the database. Here, we have:

• Employee table
• Department table

Attributes (Columns)

• Each entity has attributes (columns):

Relationship

• Each Employee belongs to one Department
• Each Department has many Employees.
• This is a One-to-Many (1:M) relationship.

Mermaid ER Diagram

erDiagram
  Employee {
    INTEGER id PK
    STRING name
    INTEGER dept_id FK
  }
  Department {
    INTEGER dept_id PK
    STRING name
  }
  Employee }o--|| Department : "works_in"

Explanation of the Arrows

• }o--|| → One-to-Many (1:M)
• One Department (||) can have many Employees (}o).
• Each Employee belongs to one Department.