Relational Databases: Creating Relationships

Understanding Relationships in Relational Databases

Relationships in relational databases are the associations between tables.
These relationships allow the database to effectively organise, store and retrieve interconnected data without unnecessary redundancy.

One-to-One Relationships

A one-to-one relationship occurs when each record in one table corresponds to exactly one record in another table.

One-to-Many Relationships

A one-to-many relationship occurs when a single record in one table is linked to multiple entries in another table.

Many-to-Many Relationships

A many-to-many relationship occurs when a single record in one table can be related to multiple records in a separate table, and vice versa.

Primary and Foreign Keys

Primary key is a unique identifier for records in a table. Each table should have a primary key.
A foreign key is a field (or collection of fields) in one table that identifies a record of another table. It’s used to establish a link between the data in two tables.

Creating Relationships in Database Software

In most database software, relationships can be established through the Relationships window or the Database Diagram tool.

The Importance of Indexing in Relationships

Indexes in a database are used to speed up searches and queries.
Building indexes on the primary key and foreign key columns of the tables involved in a relationship can greatly improve performance.

Normalisation Process

Normalisation is the process of efficiently organising data in a database, which includes the creation and honing of table relationships.
The goals of normalisation include avoiding data redundancies, ensuring data accuracy and integrity, and optimising database performance.

Testing Relationships

Once relationships are created, they should be tested thoroughly to ensure they are functioning as expected.
Testing involves entering data, modifying data, and deleting data, then analysing the effects on the related tables.