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What is a Candidate Key?

R. Woodard
R. Woodard

A candidate key is what is known as an “attribute” in advanced information management systems. It’s a very important part of many online and computer-based data sets, and is often one of the main ways in which separate accounts, divisions, or functions are differentiated on a technical level. Understanding exactly how this key works requires a bit of technical savvy. In its most basic sense, though, it’s a series of codes in a table that leads to a defined function that allows different branches, or “candidates,” of a common digital stem to maintain separate identities, at least where computer recognition is concerned.

Basic Context

Man holding computer
Man holding computer

In terms of relational database management systems, a candidate key is an attribute that is used to uniquely identify a database row entry within a table. A relational database management system is a type of database that is widely used to create collections of information that are organized based on providing relationships between different elements within the database table. Similarly, a key is a tool that allows entities to be identified. Each table can have one or more candidate-type keys, and one of these is usually set as a primary key. The primary key is a column that defines all of the rows.

Almost every type of digitized database uses this sort of key-based system to function. Big databases like online banking applications, digitized library files, and Internet-based e-mail systems are some of the most obvious places to find code-based keys in action, but they operate almost constantly in most computer functions. Even personal computers often use this sort of algorithm to store information on a hard drive or to create backup copies. These and most other internal processes happen silently and swiftly behind the screen and behind the scenes, and people without technical knowledge often have no idea they’re executing at all.

Relationship to the Superkey

In most cases, a candidate key is a subset of something called a “superkey.” A superkey is a type of identifier that attaches to an entity in a database table. Taking a business setting as an example, a superkey might be a column labeled something like VEND_CODE, which would denote a specific vendor code for a business database table. The minimum number of columns needed to make each row unique is the part of the superkey that might count as a candidate sort of key, too. In this case, if every VEND_CODE is unique, it could be the key.

Code Fields

Any time there is a field of codes, individual identifiers could work both as candidate and primary keys. In this context, the goal of each is usually to make sure that a database does not have rows that are redundant, which is to say that each row has some element in it that makes it unique. It is important that the database creator choose something that is unique to that table when choosing the key to be the candidate. As with the above example of a business database, one could use a business name as a key. If several businesses, perhaps located in different countries, have the same name, however, that identifier would not be unique and could accordingly not be used in a database that both businesses might be trying to access simultaneously.

Importance of a Unique Key

Choosing a unique candidate key is very important. Companies may share the same name, and people who are looking to open things like accounts or profiles often have first and last names that are the same or similar as well. By having the unique key and making one of those a primary key, finding a certain vendor or person by a unique key is easier. Sometimes names or known word codes can be assigned by human technicians, but numeric patterns generated by computer will also work. When every entry in the table has some key that makes it unique, it is possible to distinguish between entries that contain similar information. The system then works quickly and efficiently, which is the goal in most instances.

Discussion Comments


I have to wonder if there are really people sophisticated enough to design malware, trojans, and other programs that can hack into or take over these kinds of systems then why would one go this route when building a network or designing a company's infrastructure? Surely the ease and instant access to any number of values for a particular employee might be handy to have but when you leverage it against a possible SQL injection then the ease factor starts to look a little less appealing.


@Contentum - This is some form of a database language. There are quite a few different ones out there but SQL is the most prevalent, at least from what I've seen and read. I'm not sure what those numbers would be globally, but I'm sure it might be similar to NYC. I will agree with you that it sometimes can be confusing.


This sounds like something I once read from a SQL learning guide. Lots of columns and values. I didn't understand it then but I think now if I had to I would be able to work within its parameters with ease.

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