This document discusses different types of database relationships: one-to-one, one-to-many, and many-to-many. A one-to-one relationship links one record in one table to one record in another table. A one-to-many relationship links one record in one table to multiple records in another table. An example is a school employing multiple teachers. A many-to-many relationship links multiple records in one table to multiple records in another table, like students taking multiple subjects, but these cannot be directly implemented and must be resolved to one-to-many relationships.

1. HIGHER DATABASES
RELATIONSHIPS

2. WHAT IS A DATABASE RELATIONSHIP?
• A relationship is the way we describe how data is related or
attached to each other.
• For example we can say in a database of a school. Pupils and
teachers are related as a pupil is taught by teachers, and a
teacher teaches pupils.

3. ONE TO ONE RELATIONSHIP
•In a one – to - one relationship, each entity
occurrence in an entity is associated with one,
and only one, entity occurrence within a related
entity.
•For example, a School is managed by one, and
only one, Headteacher, with a Headteacher
managing one, and only one, School.

4. ONE TO ONE EXAMPLES
• A football club will only have one manager. A manager will only
work for one football club
• A pupil will only have one candidate number. A candidate
number can only be used by one pupil.

5. ONE TO MANY RELATIONSHIP
• In a one -to-many relationship, each entity occurrence in an
entity can be associated with one or more entity occurrences in
a related entity.
• For example, a School employs many Teachers and each of
those Teachers is employed by one School.

7. MANY TO MANY RELATIONSHIP
• In a many-to-many relationship, several entity occurrences in
an entity can be associated with multiple entity occurrences in a
related entity.
• For example, many Students study several different Subjects
and each of those Subjects is studied by many Students.
• Direct many-to-many relationships between two entities
cannot be implemented by a relational database system. To
overcome this many to many relationships are resolved to one
to many relationships