this is the link between two different tables in a relational database.
- Primary Key: the field that uniquely identifies a record in a relational database is linked to a foreign key in another table to form a relationship between the tables.
- Foreign Key: a field in one relational database table that corresponds to the primary key in another table in the database and is used to form the relationship between the two tables.
- Compound Key: where more than one field is used to uniquely identify a record in a table - often each individual field is also acting as a foreign key to seperate tables.
- One-to-one: each record in a table is related to one other record in another table.
- One-to-many: each record in a table is related to more than one record in another table.
-Many-to-many: many records in one table are related to many records in another table.
Entity Relationship Diagram: a diagram showing the tables makingup a relational database with the primary keys linking to the corresponding foreign keys and the types of relationships involved.
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