What is an Alternate Key in SQL?

Alternate keys are an essential concept in relational database management systems. AK is an alternative to primary keys and help to ensure data integrity and efficiency in searching and sorting data. But what exactly is an alternate key, and how does it work? In this article, you will learn alternate keys, exploring their definition, characteristics, and significance in the field of DBMS.

What is an Alternate Key?

Alternate keys are attributes or a combination of attributes that uniquely identify a record in a database table. Every database table has a primary key that uniquely identifies each record in the table. However, tables can also have alternate keys, which provide an alternative way to identify records in the table. Alternate keys are not used for FK like PK, but they can be used as an index in a table.

Types of Alternate Keys

There are two types of alternate keys-

1. Unique Alternate Key – This type of alternate key is unique, and no two records can have the same value. It is often used as a reference to link tables in a database.
2. Non-Unique Alternate Key – This type of alternate key is not unique, and more than one record can have the same value. It is often used in conjunction with other columns to form a unique identifier.

What is a Unique Alternate Key?

A Unique Alternate Key is a type of alternate key that ensures that each record in a database table has a unique value. It is often used as a reference to link tables in a database. Let’s take an example of a Unique Alternate Key as follows –

Suppose we have a database table named “Employees,” and we want to add a Unique Alternate Key to it. We can use the following SQL syntax to add the Unique Alternate Key

Syntax:

ALTER TABLE Employees ADD CONSTRAINT AK_Employees_EmpID UNIQUE (EmpID);

In this syntax, “AK_Employees_EmpID” is the name of the Unique Alternate Key, and “EmpID” is the name of the column in the “Employees” table that we want to use as the Unique Alternate Key.

Once we have added the Unique Alternate Key, we can use it to link other tables to the “Employees” table. For example, if we have another table named “Tasks” that has a foreign key column named “EmpID,” we can use the Unique Alternate Key in the “Employees” table to link the two tables as follows –

Syntax:

CREATE TABLE Tasks (
TaskID int PRIMARY KEY,
Description varchar(255),
EmpID int,
FOREIGN KEY (EmpID) REFERENCES Employees (EmpID)
);

In this syntax, we have created a foreign key constraint on the “EmpID” column in the “Tasks” table that references the Unique Alternate Key in the “Employees” table. This ensures that each “Task” record is linked to a unique “Employee” record.

Overall, Unique Alternate Keys are an important key in database management that can help to ensure data integrity and improve data retrieval efficiency.

What is Non-Unique Alternate Key?

A Non-Unique Alternate Key is a type of alternate keys that allows duplicate values in a database table. It can be used as a secondary key to improve query performance or to enforce certain business rules. Here is an example of a Non-Unique Alternate Keys as follows – Suppose we have a database table named “Products,” and we want to add a Non-Unique Alternate Keys to it. We can use the following SQL syntax to add the Non-Unique Alternate Keys-

Syntax:

ALTER TABLE Products ADD CONSTRAINT AK_Products_SKU UNIQUE NONCLUSTERED (SKU);

In this syntax, “AK_Products_SKU” is the name of the Non-Unique Alternate Keys, and “SKU” is the name of the column in the “Products” table that we want to use as the Non-Unique Alternate Keys. The “NONCLUSTERED” keyword specifies that the index created for the Non-Unique Alternate Keys will be a non-clustered index.

Once we have added the Non-Unique Alternate Keys, we can use it to improve query performance. For example, if we frequently search for products by their SKU value, we can use the Non-Unique Alternate Keys to create an index on the “SKU” column as follows –

Syntax:

CREATE NONCLUSTERED INDEX IX_Products_SKU ON Products (SKU);

In this syntax, we have created a non-clustered index on the “SKU” column in the “Products” table. This index will improve query performance when searching for products by their SKU value.

Overall, Non-Unique Alternate Keys are a useful tool in database management that can help to improve query performance and enforce business rules. However, it is important to use them judiciously and to ensure that they do not compromise data integrity.

How does Alternate Keys work in DBMS?

In a database management system (DBMS), an alternate key works by providing an additional unique identifier for a table. An alternate key is a column or group of columns in a table that have unique values for each row, just like a primary key. However, unlike a primary key, an alternate key does not serve as the main identifier for a table.

When a query is performed on a table that has an alternate key, the DBMS uses the alternate keys to help locate the relevant records. The alternate key is indexed in much the same way as a primary key, allowing for efficient lookup and retrieval of data. This can help to improve query performance and make the database more efficient overall.

One of the keys benefits of using alternate keys in a DBMS is that they help to ensure data integrity. By requiring that each row in a table have a unique value in the alternate keys column, you can prevent duplicate data from being entered into the table. This helps to ensure that the data is accurate and consistent, which is essential for effective database management.

How to Implement Alternate Keys in SQL?

Implementing alternate keys in SQL involves creating a unique constraint on one or more columns in a table. Refer to the below steps to implement alternate keys in SQL –

1. Identify the column or columns that will be used as the alternate keys. These should be columns that have unique values for each record in the table.
2. Create a unique constraint on the column or columns. This can be done using the ALTER TABLE statement with the ADD CONSTRAINT clause.

For example, if we have a table named “Customers” with a column named “Email” that we want to use as the alternate keys, we can use the following SQL statement to create the unique constraint-

Syntax:

ALTER TABLE Customers ADD CONSTRAINT UQ_Customers_Email UNIQUE (Email);

In this example, “UQ_Customers_Email” is the name of the unique constraint, and “Email” is the name of the column we want to use as the alternate keys.

3. Test the alternate keys by trying to insert a record with a duplicate value for the alternate keys column. If the unique constraint is working correctly, the insert statement should fail and return an error.

For example, if we try to insert a new record into the “Customers” table with an email address that already exists in the table, we should receive an error message indicating that the insert violated the unique constraint.

By implementing alternate keys in SQL, we can ensure data integrity, improve query performance, and enforce business rules. It is important to choose the appropriate column or columns for the alternate keys and to test the unique constraint thoroughly to ensure that it is working correctly.

Benefits of using an Alternate Keys

Refer to the below benefits of using Alternate Keys –

1. Efficient Data Retrieval – The alternate keys provides an additional index that allows for efficient data retrieval, especially when searching for records based on non-primary keys fields.
2. Improved Data Integrity – The use of alternate keys ensures that each record in a database is uniquely identified, thereby reducing the chances of data redundancy and data inconsistency.
3. Simplified Data Management – The alternate keys provides an alternative way of accessing records in a database, which simplifies data management and improves overall system performance.
4. Flexibility – The use of alternate keys provides flexibility in the design of a database, making it easier to adapt to changing business needs.

Examples of Alternate Keys

Here are some examples of alternate keys in a database-

1. Email address- In a user table, the email address column could be alternate keys. Since each user must have a unique email address, this column can be used as alternate keys to enforce this constraint.
2. Social security number- In an employee table, the social security number column could be alternate keys. Since each employee must have a unique social security number, this column can be used as alternate keys to enforce this constraint.
3. ISBN number- In a book table, the ISBN number column could be alternate keys. Since each book must have a unique ISBN number, this column can be used as alternate keys to enforce this constraint.
4. Order number- In an order table, the order number column could be alternate keys. Since each order must have a unique order number, this column can be used as alternate keys to enforce this constraint.
5. Username- In a user table, the username column could be alternate keys. Since each user must have a unique username, this column can be used as alternate keys to enforce this constraint.

In each of these examples, the alternate keys helps to enforce a unique constraint on a column that is important to the business logic of the database. By using alternate keys, you can improve data integrity and prevent data duplication, which can lead to more accurate and efficient database management.

Advantages of Using Alternate Keys

Refer to the below some of the advantages of using Alternate Keys –

1. Alternate keys help to ensure that data in a table is unique and consistent. This helps to improve data integrity and prevents data duplication, which can lead to inaccurate data.
2. Using alternate keys can help to improve query performance. By using an alternate key in a WHERE clause, the database can quickly locate the relevant records without having to perform a full table scan.
3. Creating an index on an alternate key can help to improve database performance by making it faster to locate and retrieve records. This can lead to faster query times and better overall performance.
4. By using alternate keys, it is easier to manage and update data in a database. This can lead to more efficient database management and faster development cycles.

Disadvantages of Using Alternate Key

Refer to the below some of the disadvantages of using Alternate Keys –

1. Using alternate keys can increase the storage requirements of a database. Since each unique value requires its own storage space, using alternate keys can cause a database to become larger and more complex.
2. While alternate keys can improve query performance in some cases, they can also have a negative impact on performance if not used correctly. Creating too many alternate keys or using them incorrectly can lead to slower query times and other performance issues.
3. Alternate keys can add complexity to a database design. Managing multiple unique constraints and alternate keys can be challenging and requires careful planning and design.
4. Using alternate keys requires ongoing maintenance to ensure that they are working correctly. This can add additional overhead to database management and may require additional resources.

Best Practices for Using Alternate Key

Using alternate keys in a database requires careful consideration and planning to ensure the best possible results. Refer to the below for some best practices for using alternate keys-

1. Choose the right column or columns- When selecting columns for an alternate keys, choose columns that have unique values for each record in the table. This will help to ensure data integrity and prevent data duplication.
2. Avoid using columns that may change- Avoid using columns that may be subject to change, such as names or addresses. This can cause issues with the unique constraint and may require updates to other tables.
3. Use descriptive names for constraints- Use descriptive names for alternate keys constraints to make them easy to identify and manage. For example, instead of using “AK1”, use a name that reflects the purpose of the alternate keys.
4. Test the alternate keys thoroughly- Test the alternate keys thoroughly to ensure that it is working correctly. This includes testing for data duplication and verifying that the unique constraint is enforced.
5. Use indexes to improve performance- Create indexes on alternate keys to improve query performance. This can help to speed up searches and reduce the time required to retrieve data.
6. Be consistent with naming conventions- Use consistent naming conventions for alternate keys across tables to make them easy to identify and manage. This can help to ensure consistency and make it easier to maintain the database over time.

By following these best practices, you can ensure that alternate keys are used effectively and efficiently in your database design. This will help to improve data integrity, performance, and overall database management.

Common mistakes About Alternate Key

While alternate keys can provide many benefits in database design, there are also some common mistakes that can be made. Refer to the below some common mistakes to avoid when working with alternate keys-

1. Using columns that are not unique- Alternate keys must be made up of one or more columns that have unique values for each record in the table. If a non-unique column is used as alternate keys, it can lead to data duplication and other issues.
2. Using columns that can change- Using columns that can change, such as names or addresses, can cause issues with the unique constraint and may require updates to other tables. It is best to avoid using columns that are subject to change as alternate keys.
3. Failing to test the alternate keys- It is important to thoroughly test the alternate keys to ensure that it is working correctly. This includes testing for data duplication and verifying that the unique constraint is enforced.
4. Not using indexes- Creating an index on the alternate keys can improve query performance and reduce the time required to retrieve data. Failing to create an index can lead to slow query times and other performance issues.
5. Inconsistent naming conventions- Using inconsistent naming conventions for alternate keys across tables can make it difficult to identify and manage them. It is best to use a consistent naming convention to ensure clarity and consistency across the database.
6. Overusing alternate keys- While alternate keys can be useful in many cases, it is important to avoid overusing them. Using too many alternate keys can lead to increased storage requirements and may impact performance.

By avoiding these common mistakes, you can ensure that your alternate keys are effective and efficient in improving data integrity and performance in your database.

FAQs

Conclusion

The alternate key is an essential component of database that offers numerous benefits, including efficient data retrieval, integrity, and flexibility. By understanding the alternate key, database managers can design more robust databases that can easily adapt to changing business needs. Therefore, it is essential to consider the use of alternate keys in designing databases to ensure optimal system performance. We hope you would have liked this very well.

Please share this on your social network so that it can be available to even more needy persons. If you have any questions, feedback, or suggestions regarding this tutorial, please contact us. Do comment right in the comments section below. We will consider your valuable input and try to give you a response asap.

Recommended Article Posts

DDL Full Form and How is it used in SQL?	DML Full Form and How is it used in SQL?
DCL Full Form and How is it used in SQL?	TCL Full Form and How is it used in SQL?
What is DQL in SQL?	Key Constraints in DBMS With Fundamentals
Primary Key Constraint in SQL	Unique Key in DBMS and Best Practices
Foreign Key in DBMS and Best Practices	What is a Super Key in DBMS?
What is Check Constraint in SQL?	What is Not Null Constraint in SQL?
What is a Candidate Key in DBMS?	What is Default Constraint in SQL?