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Database Relationships - Coggle Diagram
Database Relationships
Reation Keys
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Foreign Key
An attribute of a table that is also a primary key in another table. This establishes a link, or relationship, between these two tables.
Super Key
Any attribute, or group of attributes, that can uniquely identify a tuple in a relation.
Integrity Constraints
Referential Integrity
This rule states that every foreign key value must match the primary key value of a record in another table, or must be null.
Entity Integrity
This rule states that every entity (table) must have a primary key field and the data in that primary key field must be unique to each record.
Entity Relationships
One-to-One
A single record of a table is related to a single record of another table. This could be the relationship between a person and their passport.
Many-to-Many
More than one record of a table is related to more than one record of another table. This could be the relationship between students and their courses.
One-to-Many
A single record of a table is related to more than one record in another table. In this relationship the foreign key would appear in the many side of the relationship. This could be the relationship between a customer and their orders