Symbols from MySQL Entity Relationship Diagrams

Entitities

primary key

optional foreign key

required foreign key

optional attribute

required attribute

Example Entity

An entity drawn by MySQL Workbench with a primary key, an optional foreign key, three required foreign keys, an optional attribute, and three required attributes.

Relationships

Relationship Ends

zero or one (optional)

one and only one (required)

zero or many (optional)

one or many (required)

One-to-One Relationships

zero or one (optional) to zero or one (optional)

one and only one (required) to zero or one (optional)

zero or one (optional) to one and only one (required)

one and only one (required) to one and only one (required)

One-to-Many Relationships

zero or one (optional) to zero or many (optional)

one and only one (required) to zero or many (optional)

zero or one (optional) to one or many (required)

one and only one (required) to one or many (required)