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ER diagram

Entity-relationship diagrams describe a database schema: entities, their attributes, and the cardinality of the relationships between them. zombie-mermaid renders the full crow’s-foot notation along with PK/FK/UK key badges on typed attributes.

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A schema's entities, and how they relate.

schema.mmd
erDiagram
  CUSTOMER ||--o{ ORDER : places
ER diagram diagram, zombie-mermaid CUSTOMER (no attributes) ORDER (no attributes) places
More examples

More real-world examples.

ER diagram diagram, zombie-mermaid CUSTOMER PK int id string name UK string email date created_at
ER: Entity with Attributes
ER diagram diagram, zombie-mermaid ORDER PK int id FK int customer_id UK string invoice_number decimal total date order_date string status
ER: Attribute Keys (PK, FK, UK)
ER diagram diagram, zombie-mermaid A (no attributes) B (no attributes) C (no attributes) D (no attributes) E (no attributes) F (no attributes) G (no attributes) H (no attributes) one-to-one one-to-many opt-to-many many-to-many
ER: All Cardinality Types
ER diagram diagram, zombie-mermaid ORDER (no attributes) LINE_ITEM (no attributes) SHIPMENT (no attributes) PRODUCT (no attributes) REVIEW (no attributes) contains ships-via includes receives
ER: Mixed Identifying & Non-Identifying
ER diagram diagram, zombie-mermaid CUSTOMER PK int id string name UK string email ORDER PK int id date created FK int customer_id PRODUCT PK int id string name float price LINE_ITEM PK int id FK int order_id FK int product_id int quantity places contains includes
ER: E-Commerce Schema
ER diagram diagram, zombie-mermaid USER PK int id UK string username UK string email date joined POST PK int id string title text content FK int author_id date published COMMENT PK int id text body FK int post_id FK int user_id date created TAG PK int id UK string name writes authors has tagged-with
ER: Blog Platform Schema
Show 1 more example
ER diagram diagram, zombie-mermaid STUDENT PK int id string name date dob string grade TEACHER PK int id string name string department COURSE PK int id string title FK int teacher_id int credits ENROLLMENT PK int id FK int student_id FK int course_id string semester float grade teaches enrolled has
ER: School Management Schema
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