Some examples of how to use the as-yet undocumented PlantUML ERD functionality.

ERD-Example.puml

@startuml
hide circle
hide empty members

' PlantUML ERD examples worked out from:
' https://github.com/plantuml/plantuml/pull/31

together {
    ' zero or one
    foo1 -o| bar1

    ' exactly one
    foo2 --|| bar2

    ' zero or many
    foo3 -o{ bar3

    ' one or many
    foo4 -|{ bar4

    ' you can combine any of these at both ends
    foo5 ||-|{ bar5
}

entity User {
    **id** int [PRI]
    other_key guid
    --
    **group_id** int [FK]
    --
    **email** [UNIQ]
    firstname varchar(255)
    lastname varchar(255)
    created_at datetime
    updated_at datetime
    ...
}

entity Group {
    **id** int [PRI]
    --
    ...
}

Group -o{ User

@enduml