Mermaid ER Diagram

Design database schemas with entity relationship diagrams. Model tables, relationships, and data structures for your applications.

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Quick Syntax Reference

Learn the essential syntax for creating entity relationship diagrams.

Entity DefinitionDefine entities with attributes

erDiagram
  USER {
    int id PK
    string name
    string email
  }

RelationshipsConnect entities with cardinality

erDiagram
  USER ||--o{ ORDER : places
  ORDER ||--|{ ITEM : contains

CardinalityRelationship types

||--||  one to one
||--o{ one to many
}o--o{ many to many

Data TypesCommon attribute types

int, string, text, boolean
date, datetime, float, blob

KeysPrimary and foreign keys

PK - Primary Key
FK - Foreign Key
UK - Unique Key

Relationship LabelsDescribe relationships

USER ||--o{ ORDER : "places"
CUSTOMER ||--|{ ACCOUNT : "owns"

ER diagrams are essential for database design and data modeling in software projects.

Design relational database schemas before implementation.

Model complex data relationships and constraints.

Document existing database structures for teams.

Plan database migrations and schema changes.

Design data models for REST or GraphQL APIs.

Map data flows between different systems.