What are the SQL Alternate Key?



Keys are an essential a part of SQL, and the first, international, and candidate keys maintain a major worth. The alternate key holds are essential, but we frequently overlook their significance. They’re used to design our database, Make sure the integrity of our knowledge, and create an environment friendly strategy to retrieve data. Intriguing proper? Additional on this article, we’ll talk about SQL Alternate Key intimately.

SQL Alternate Keys


  • Perceive the aim and fundamental syntax of the alternate key.
  • Determine situations the place the Alternate key could be utilized successfully.
  • Implement the alternate key to keep away from inconsistency and depletion of integrity.
  • Use instances of alternate keys and some great benefits of having an alternate key.

What’s an alternate key?

In easy phrases, an Alternate secret is a candidate key that isn’t a major key. Everybody is aware of that the first key uniquely identifies every report within the desk. The alternate key additionally uniquely identifies the data within the desk and holds the identical function. 

Vital features of alternate key

  • Knowledge Integrity – This ensures that every row in our desk is exclusive
  • Knowledge retrieval –  Supplies further distinctive columns that can be utilized for retrieving knowledge effectively
  • Redundancy Elimination – By guaranteeing that columns are distinctive, we cut back redundancy. 

Syntax for creating alternate keys

Creating an alternate secret is making columns with distinctive constraints. 

ALTER TABLE table_name
ADD CONSTRAINT constraint_name UNIQUE (column1, column2, ...);

Creating alternate keys

Let’s first create a desk to find out about alternate keys. 

    Electronic mail VARCHAR(255) NOT NULL,
    FirstName VARCHAR(50),
    LastName VARCHAR(50)
SQL Alternate Keys

Right here, we are able to see that EmployeeID is our major key. We additionally know two workers can’t have the identical e-mail deal with and SSN. Therefore, we now have to implement distinctive constraints for them. 


ADD CONSTRAINT unique_email UNIQUE (Electronic mail);
SQL Alternate Keys

The above code will make Electronic mail and SSN distinctive. This makes them an alternate key to the desk College students.

Use instances of Alternate key

  • Distinctive person identifiers – From the above instance, Electronic mail and EmployeeID can be utilized to determine distinctive workers in person administration programs. This enhances the retrieval when EmployeeID isn’t recognized,
  • Stock System – Product codes and serial numbers can each uniquely determine objects.
  • Scholar Data – StudentID and PhoneNumber can each act as distinctive identifiers.

Additionally learn: SQL: A Full Fledged Information from Fundamentals to Superior Degree

Some samples with Worker Desk

Let’s attempt inserting some pattern knowledge into our Worker desk. 

INSERT INTO Workers (EmployeeID, SSN, Electronic mail, FirstName, LastName) 
VALUES (1, '123-45-6789', '[email protected]', 'John', 'Doe');

INSERT INTO Workers (EmployeeID, SSN, Electronic mail, FirstName, LastName) 
VALUES (2, '987-65-4321', '[email protected]', 'Jane', 'Doe');
SQL Alternate Keys

From the above two codes, we are able to see there isn’t a downside, and the code is getting executed. 

INSERT INTO Workers (EmployeeID, SSN, Electronic mail, FirstName, LastName) 
VALUES (3, '123-45-6789', '[email protected]', 'John', 'Smith');
SQL Alternate Keys

We are able to see that this fails because the SSN have to be distinctive; let’s attempt an analogous factor with e-mail

INSERT INTO Workers (EmployeeID, SSN, Electronic mail, FirstName, LastName) 
VALUES (4, '555-55-5555', '[email protected]', 'Johnny', 'Doe');
SQL Alternate Keys

We are able to see that this fails as the e-mail needs to be distinctive, [email protected] is already current in our database. 

Additionally learn: SQL For Knowledge Science: A Newbie Information!

Benefits of Utilizing Alternate Keys

  • Enhanced Knowledge Integrity: Ensures that crucial columns stay distinctive.
  • Flexibility in Knowledge Retrieval: Permits for a number of distinctive columns for querying.
  • Higher Indexing: Improves search effectivity with a number of distinctive indexes.


Alternate key performs an essential function within the SQL and database administration programs. We must always attempt implementing and utilizing them to boost integrity and adaptability. We are able to guarantee a sturdy and versatile database with an understanding of alternate keys. 

Steadily Requested Questions

Q1. What’s an alternate key in SQL?

Ans. Any candidate key which isn’t a major secret is an alternate key.  

Q2. How is an alternate key completely different from a major key?

Ans. There’s much less distinction within the performance of alternate and first keys. A candidate key, which isn’t a major key, is an alternate key. Each determine data uniquely.

Q3. What’s a candidate key?

Ans. A candidate secret is a minimal attribute that uniquely identifies a report.

This fall. What’s a brilliant key?

Ans. A brilliant secret is any mixture of attributes uniquely figuring out a report, together with candidate keys.