Mermaid ER Diagram Cheat Sheet

Entities, their columns, and the cardinalities between them.

Every picture on this page was drawn by

Mernyx, the native Mermaid editor for macOS. Not by a browser running Mermaid.js — the same renderer the app uses for its canvas.

Entities and attributes

Curly braces hold the columns. The type comes first, then the name.

erDiagram
  CUSTOMER {
    string name
    string email
  }
  ORDER {
    int orderNumber
    date placedAt
  }

PK, FK and UK mark the primary, foreign and unique keys.

erDiagram
  CUSTOMER {
    string custNumber PK
    string email UK
  }
  ORDER {
    int orderNumber PK
    string custNumber FK
  }

The marks at each end say how many. A bar is one, a crow's foot is many.

erDiagram
  CUSTOMER ||--o{ ORDER : places
  ORDER ||--|{ LINE_ITEM : contains
  PRODUCT }o--o{ TAG : tagged

The text after the colon is the verb between the two entities. More than one word needs quotes.

erDiagram
  CUSTOMER ||--o{ ORDER : "places an order"
  ORDER ||--|{ LINE_ITEM : contains