How is data redundancy avoided in database design?

Data redundancy in database design is avoided through normalisation, use of primary keys, and establishing relationships between tables.

Normalisation is a systematic approach of decomposing tables to eliminate data redundancy and undesirable characteristics like insertion, update and deletion anomalies. It is a multi-step process that puts data into tabular form, removing duplicated data from the relation tables. Normalisation is used for mainly two purposes, eliminating redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.

Primary keys are another method used to avoid data redundancy. A primary key is a unique identifier for a record in a table. By ensuring that each record has a unique identifier, it prevents duplicate records from being entered into the table. This not only helps to reduce redundancy but also aids in data retrieval and manipulation. Primary keys can be a single field or a combination of fields, as long as the combination is unique.

Establishing relationships between tables is another way to avoid data redundancy. In a relational database, tables are linked to each other through foreign keys. A foreign key in one table points to a primary key in another table. This allows data to be organised more efficiently and reduces the need for duplicate data. For example, instead of having a customer's address details stored in multiple tables, a single table can be created to store these details. Other tables can then reference this table using a foreign key, eliminating the need to store the same data multiple times.

In conclusion, avoiding data redundancy in database design is crucial for efficient data management. It not only saves storage space but also makes data manipulation and retrieval more efficient. Normalisation, use of primary keys, and establishing relationships between tables are some of the key methods used to achieve this.