KEYS IN DATABASES

6 min readOct 1, 2023

Keys in Database Use

Keys in a database are used to uniquely identify rows (or tuples) in a table (or relation). They are essential for ensuring the integrity and accuracy of data and for enabling efficient data retrieval and manipulation.

There are several different types of keys in a database, each with its own specific purpose. The most common types of keys are:

Candidate keys: A candidate key is a set of attributes that uniquely identify each row in a table.
Primary key: The primary key is a single candidate key that is chosen to be the primary identifier for a table.
Foreign key: A foreign key is a column in one table that references the primary key of another table. This creates a relationship between the two tables, allowing data to be linked and shared.
Alternate key: An alternate key is a candidate key that is not chosen to be the primary key. It can still be used to uniquely identify rows in the table, but it is not enforced by the database management system (DBMS).
Composite key: A composite key is a key that consists of two or more attributes.
Surrogate key: A surrogate key is a column that is added to a table to serve as the primary key, even if it is not a natural identifier for the rows in the table.

Candidate Keys

A candidate key is a set of attributes that uniquely identify each row in a table. For example, in a table of customer records, the candidate keys might be the customer ID, the customer name, or the customer email address.

Primary Key

The primary key is a single candidate key that is chosen to be the primary identifier for a table. The primary key is enforced by the DBMS, meaning that no two rows in the table can have the same primary key value.

The primary key is typically used to index the table, which allows the DBMS to quickly find rows in the table based on their primary key values.

Foreign Key

A foreign key is a column in one table that references the primary key of another table. This creates a relationship between the two tables, allowing data to be linked and shared.

For example, a customer orders table might have a foreign key that references the customer ID column in the customer table. This allows the database to track which orders belong to which customers.

Alternate Key

An alternate key is a candidate key that is not chosen to be the primary key. It can still be used to uniquely identify rows in the table, but it is not enforced by the DBMS.

Alternate keys can be useful for creating secondary indexes on tables, which can improve the performance of certain database queries.

Composite Key

A composite key is a key that consists of two or more attributes. For example, a table of product records might have a composite key consisting of the product ID and the product category.

Composite keys can be useful when there is no single attribute that uniquely identifies each row in the table.

Surrogate Key

A surrogate key is a column that is added to a table to serve as the primary key, even if it is not a natural identifier for the rows in the table. Surrogate keys are often used in data warehouses and other data integration systems.

Benefits of Using Keys in Databases

There are several benefits to using keys in databases:

Data integrity: Keys help to ensure the integrity of data by preventing duplicate rows from being inserted into a table and by ensuring that foreign key values are valid.
Efficient data retrieval and manipulation: Keys can be used to create indexes on tables, which can improve the performance of database queries and other data manipulation operations.
Data sharing and integration: Keys can be used to create relationships between tables, which allows data to be shared and integrated more easily.

Best Practices for Using Keys in Databases

When using keys in databases, it is important to follow certain best practices:

Choose the right key type: When choosing a key type for a table, it is important to consider the specific needs of the database application. For example, if the key will be used to index the table, then a composite key should be avoided, as composite keys can make indexes less efficient.
Enforce key constraints: It is important to enforce key constraints in the database to ensure the integrity of data. This can be done using the DBMS or by writing application code to enforce the constraints.
Use surrogate keys for primary keys. When possible, it is best to use surrogate keys for primary keys. This is because surrogate keys are less likely to change than natural keys, which can improve the performance and maintainability of the database.

Why are keys important in databases?

Keys are important in databases for a number of reasons:

Data integrity: Keys help to ensure the integrity of data by preventing duplicate rows from being inserted into a table and by ensuring that foreign key values are valid. For example, if the primary key for a table of customer records is the customer ID, then the database will not allow two rows to be inserted with the same customer ID. This helps to ensure that the data in the table is accurate and consistent.
Efficient data retrieval and manipulation: Keys can be used to create indexes on tables, which can improve the performance of database queries and other data manipulation operations. For example, if a table of product records has an index in the product ID column, then the database can quickly find the row for a particular product by its product ID value. This can improve the performance of queries that return specific products, such as a query to find all products in a particular category.
Data sharing and integration: Keys can be used to create relationships between tables, which allows data to be shared and integrated more easily. For example, a table of customer orders might have a foreign key that references the customer ID column in the customer table. This allows the database to track which orders belong to which customers. This information can then be used to create reports and other analyses that combine data from both tables.

Example

Consider the following table of customer records:

customer_id | customer_name | customer_email
------------- | -------------- | --------------
1            | Alice Smith   | alice.smith@example.com
2            | Bob Jones     | bob.jones@example.com
3            | Carol Williams | carol.williams@example.com

The primary key for this table is the customer_id column. This is because thecustomer_id value uniquely identifies each customer in the table.

Thecustomer_email column is a candidate key for this table because it also uniquely identifies each customer in the table. However, it is not the primary key.

Now, consider the following table of order records:

order_id | customer_id | product_id
-------- | -------------- | ----------
1        | 1            | 100
2        | 2            | 200
3        | 3            | 300

The foreign key in this table is the customer_id column. This column references the primary key in the customer table. This creates a relationship between the two tables, allowing us to track which orders belong to which customers.

Here is a nice video I found on Keys in DBMS

https://www.youtube.com/watch?v=JkwbhFUftSc

Conclusion

Keys are an essential part of database design. By understanding the different types of keys and how to use them effectively, database designers can create databases that are efficient, reliable, and secure.