Composite Key in Database

A database is a structured collection of data organized and stored electronically in a computer system. It is designed to efficiently manage, retrieve, and manipulate large volumes of data according to specific requirements and criteria.

In a relational database, the key plays an important role. The key is used to identify a record or a tuple of the table uniquely. Keys are also used to establish and identify the relationships between the tables.

Types of Keys in Database

• Primary Key
• Candidate Key
• Super Key
• Foreign Key
• Alternate Key
• Composite Key
• Artificial Key

Composite Key

A composite key is a candidate key consisting of two or more attributes(table columns) that uniquely identify a record/tuple (table row) or a relation. A compound key is a composite key for which each attribute that makes up the key is a foreign key in its own right.

Examples

Consider we have a table Orders with three attributes Customer id, Product id, Quantity.The key

Fig.1 Orders table

Customer id needs to be entered every time the order is placed, hence Customer id can repeat in the table and can not serve as a primary key. Also, Product id and Quantity cannot be chosen as primary key because multiple customers can buy same product and the same quantity. Here any of the three attributes can not be used as primary key, hence combination of these attributes need to be used.

For example, [Customer id + Product id] can be used to identify the records uniquely.

Fig. 2 Orders table

Syntax to Create Composite Key in mySQL

CREATE TABLE Orders

(

Customer_id INT,

Product_id INT,

Quantity INT,

PRIMARY KEY (Customer_id, Product_id)

);

How to Choose Attributes for Composite Key?

• Make sure that each record has a unique identification by combining specific attributes.
• Keep the attributes ridiculously low to have a full-fledge property.
• Determine the characters that change minimally to ensure consistent data.

Advantages of Composite Key

• Space Efficiency: Composite keys in tables save space by using current attributes. This helps store data better, especially in huge databases.
• Simplicity of Implementation: Using composite keys is simple. They use existing table attributes, so there’s no need for extra data structures or complicated indexing.
• Flexibility in Database Design: Using more than one attribute to make a unique identifier gives flexibility in database design. This flexibility can handle different data modeling needs and support complicated relationships between tables.
• Enhanced Data Integrity: Composite keys uniquely identify records by utilizing multiple attributes, which helps to maintain data integrity in the database. This minimizes the chance of duplicate records or inconsistencies, ultimately enhancing the quality of data.

Disadvantages of Composite Key

• Complexity in Querying: Complicated queries will emerge if the primary key is composite, and they will be clearly visible when working with several tables. Consequently, queries may require addition of the conditional clause to involve many attributes responsible for unique structural key. As a result, those statements are quite long and complex.
• Maintenance Challenges: Otherwise such as in cases when uncertain difference occurs to the composition key which is composed of multiple basic attributes that cannot remain unchanged like the updates or the deletions, then the main task which is to maintain data integrity becomes more difficult. The updation process could be complex if even one of the values is changed in the composite key, which may warrent updating many records across various tables that may be subject to mistake.
• Limited Flexibility: When a composite key with a set of fields that are affected by constant updates and deletions, such as data auditing, assuring data integrity becomes so troublesome. Changing the value of the composite key can occur either in the single table or in many tables, which may affect other table’s data. Furthermore, it can be difficult to spot the error if the system is complex.

Conclusion

Composite keys guarantee that every file has a unique identification, by ensuring that each record in the relational database has a clear distinction from any other record. This is true and these features can be considered both as a strength, comparing to regular text books and as a weakness, comparing to traditional text books, which are more convenient for maintenance and searching. Key composite can be used to increase data accuracy and retrieval efficiency by database systems with attention and contributed by the implementation in correct and proper ways.

Frequently Asked Questions on Composite Key – FAQs

What is a composite key?

A compound key is a compound entity which consists of two or more substance that makes it possible to identify one table row in database table. Unlike a primary key which is a single column, a composite key will be a compound column that consists of more than one column.

When is a composite key used?

Composite keys provides a solution when a single field alone cannot identify rows in a table in a unique way. They hold their main functions in many-to-many relationships and when natural keys are of use, usually for necessitating integrity.

How are composite keys different from primary keys?

The leading key is one of the types of composite keys that is not only used to store a certain entry of the table but also used to perform the operations of entity integrity. It should be noted that, of course, there are also composite keys that couldn’t function as the primary key and vice versa, in other words, every primary key is in fact a compound key. In order to make sure only one value from a column will be unique, a primary key is shown. The means of use of the keys, for the purpose of other output, which makes the column name different is known as alternate keys.

What are the advantages of using a composite key?

Composite keys give an additional flexibility to the data model by allowing to implement more complex relationships, like using them for node-edge modeling or applying associative entities feature for many-to-many relationships. Moreover, they support the usage of the natural keys which can improve data integrity through correspondence with the real world identifiers. In detail, the generated keys will be more genuine if they are adjuncts of the real world identifiers.

Can a table have multiple composite keys?

Yes, a table can have multiple composite keys. Each composite key represents a different combination of columns that uniquely identifies rows within the table. However, only one composite key can typically serve as the primary key, enforcing entity integrity.