What Is Secondary Key?

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In the world of databases, efficient data organization is paramount for optimal performance and data retrieval. One essential component of database design is the concept of keys, which facilitate the identification and linkage of data records. While primary keys serve as the unique identifier for each record, secondary keys provide additional indexing and sorting capabilities. In this blog post, we will explore the significance of secondary keys, their role in data management, and their impact on database performance.

What Is Secondary Key?

A secondary key, also known as a non-primary key, is a column or combination of columns within a database table that is used for indexing and data retrieval purposes. Unlike primary keys, secondary keys are not required to be unique for each record. They serve as supplemental identifiers, providing alternative ways to access and organize data.

Role Of Secondary Key:

  1. Data Retrieval: Secondary keys play a vital role in enhancing data retrieval efficiency. By creating an index based on a secondary key, the database management system can quickly locate and retrieve records that match specific search criteria. This helps improve query performance and reduces the need for full table scans.
  2. Sorting and Ordering: Secondary keys allow for data sorting and ordering in different ways than the primary key. They enable the database to arrange records based on specific columns, such as alphabetical order, chronological order, or numerical order. This flexibility facilitates customized data presentation and analysis.
  3. Joining Tables: Secondary keys are often used to establish relationships between tables through join operations. By matching values between secondary key columns in different tables, the database can combine data from multiple tables into a single result set. This enables complex data analysis and reporting across related entities.
  4. Constraints and Data Integrity: Secondary keys can also be used to enforce data integrity constraints in the database. For example, a unique secondary key can ensure that certain column values remain distinct within a table, preventing duplicate or inconsistent data entries.

Impact On Database Performance:

  1. Indexing Overhead: While secondary keys enhance data retrieval efficiency, they also introduce indexing overhead. Maintaining indexes requires additional storage space and imposes overhead on insert, update, and delete operations. Therefore, careful consideration should be given to the selection of appropriate secondary keys to strike a balance between indexing benefits and performance impact.
  2. Index Maintenance: As data in the table is modified, the associated indexes need to be updated to reflect the changes. This index maintenance process can impact database performance, especially in scenarios with frequent data modifications. Proper indexing strategies and periodic index optimization can mitigate the performance impact.
  3. Query Optimization: Effective utilization of secondary keys can significantly improve query performance. By analyzing query execution plans and selecting appropriate secondary keys for indexing, database administrators can optimize query performance and reduce response times.


Secondary keys are essential components of database design, providing additional indexing, sorting, and data retrieval capabilities. They enable efficient data organization, facilitate joins between tables, and ensure data integrity. While secondary keys enhance data management and retrieval, their utilization requires careful consideration to strike a balance between indexing benefits and performance impact. By leveraging secondary keys effectively, database administrators can optimize query performance and enhance the overall efficiency of the database system.

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What Is A Secondary Key Example?

Select any one of the candidate key as the primary key. Rest of the two keys would be Secondary Key. Let’s say you selected Student_ID as primary key, therefore Student_Enroll and Student_Email will be Secondary Key (candidates of primary key).

How Do You Use Secondary Keys?

To define a secondary key

Select the first empty line and then from the View menu, choose Keys. The Keys window appears. The first line shows the primary key. Enter the secondary keys on the following lines as comma-separated lists; for example: Name, Address.

What Is Alternate Key And Secondary Key?

Alternate keys are those candidate keys which are not the Primary key. There can be only one Primary key for a table. Therefore all the remaining Candidate keys are known as Alternate or Secondary keys.

What Is Secondary Key And Composite Key?

Composite Key – If any single attribute of a table is not capable of being the key i.e it cannot identify a row uniquely, then we combine two or more attributes to form a key. This is known as a composite key. Secondary Key – Only one of the candidate keys is selected as the primary key.

What Is The Difference Between Secondary Key And Foreign Key?

Secondary Key – Only one of the candidate keys is selected as the primary key. The rest of them are known as secondary keys. Foreign Key – A foreign key is an attribute value in a table that acts as the primary key in another table. Hence, the foreign key is useful in linking together two tables.

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