EDUCBA

EDUCBA

MENUMENU
  • Free Tutorials
  • Free Courses
  • Certification Courses
  • 360+ Courses All in One Bundle
  • Login
Home Data Science Data Science Tutorials SQL Tutorial SQL Super Key
Secondary Sidebar
SQL Tutorial
  • Keys
    • SQL Keys
    • SQL Foreign Key
    • Primary Key in SQL
    • Foreign Key in SQL
    • Unique Key in SQL
    • SQL UNIQUE Constraint
    • SQL Primary Key
    • Alternate Key in SQL
    • SQL Super Key
  • Basic
    • What is SQL
    • Careers in SQL
    • Careers in SQL Server
    • IS SQL Microsoft?
    • SQL Management Tools
    • What is SQL Developer
    • Uses of SQL
    • How to Install SQL Server
    • What is SQL Server
    • SQL Quick References
    • SQL Like Wildcard
    • SQL Like with Multiple Values
    • SQL Examples
    • SQL Server Versions
    • SQL DROP DB
    • SQL Case Insensitive
    • SQL Expressions
    • Database in SQL
    • SQL Data Types
    • SQL Keywords
    • Composite Key in SQL
    • SQL WAITFOR
    • SQL Constraints
    • Transactions in SQL
    • First Normal Form
    • SQL Server Data Types
    • SQL Administration
    • SQL Variables
    • SQL Enum
    • SQL GROUP BY WHERE
    • SQL ROW
    • SQL EXECUTE
    • SQL EXCLUDE
    • SQL Performance Tuning
    • SQL UUID
    • Begin SQL
    • SQL Update Join
    • SQL Between Dates
    • Cheat sheet SQL
  • Operators
    • SQL Operators
    • SQL Arithmetic Operators
    • SQL Logical Operators
    • SQL String Operators
    • Ternary Operator in SQL
  • Commands
    • SQL Commands
    • sqlplus set commands
    • SQL Alter Command
    • SQL Commands Update
    • SQL DML Commands
    • SQL DDL Commands
    • FETCH in SQL
  • Clause
    • SQL Clauses
    • SQL IN Operator
    • SQL SELECT DISTINCT Multiple Columns
    • SQL Null Values
    • SQL LIKE
    • SQL LIKE Query
    • SQL LIKE Operator
    • SQL LIKE Clause
    • SQL NOT Operator
    • SQL Minus
    • SQL WHERE Clause
    • SQL with Clause
    • SQL HAVING Clause
    • SQL HAVING Clause
    • SQL GROUP BY DAY
    • ORDER BY Clause in SQL
    • SQL ORDER BY CASE
    • SQL ORDER BY DESC
    • SQL ORDER BY DATE
    • SQL ORDER BY Alphabetical
    • SQL ORDER BY Ascending
    • SQL Order by Count
    • SQL GROUP BY Month
    • SQL GROUP BY Multiple Columns
    • SQL GROUPING SETS
  • Queries
    • SQL Insert Query
    • SQL SELECT Query
    • SQL SELECT RANDOM
    • SQL Except Select
    • SQL Subquery
    • SQL SELECT DISTINCT
    • SQL WITH AS Statement
  • Functions
    • SQL Date Function
    • SQL Server Functions
    • SQL String Functions
    • SQL Compare String
    • Timestamp to Date in SQL
    • SQL REGEX
    • SQL Window Functions
    • SQL Syntax
    • SQL CONCAT
    • SQL ALTER TABLE
    • SQL MOD()
    • SQL Timestamp
    • SQL Min and Max
    • SQL TO_DATE()
    • SQL DATEADD()
    • SQL DATEDIFF()
    • SQL HOUR()
    • SQLite? functions
    • ANY in SQL
    • LIKE Query in SQL
    • SQL NOT NULL
    • SQL NOT IN
    • SQL MAX()
    • SQL MIN()
    • SQL SUM()
    • SQL COUNT
    • SQL identity
    • SQL DELETE Trigger
    • SQL Declare Variable
    • SQL Text Search
    • SQL COUNT DISTINCT
    • SQL TEXT
    • SQL Limit Order By
    • BETWEEN in SQL
    • LTRIM() in SQL
    • TOP in SQL
    • SQL Select Top
    • Merge SQL
    • SQL TRUNCATE()
    • SQL UNION
    • SQL ALL
    • SQL INTERSECT
    • SQL Alias
    • SQL Server Substring
    • CUBE in SQL
    • SQL RANK()
    • SQL CTE
    • SQL LAG()
    • SQL MID
    • SQL avg()
    • SQL WEEK
    • SQL DELETE
    • SQL DATEPART()
    • SQL DECODE()
    • SQL DENSE_RANK()
    • SQL NTILE()
    • SQL NULLIF()
    • SQL Stuff
    • SQL Ceiling
    • SQL EXISTS
    • SQL LEAD()
    • SQL COALESCE
    • SQL BLOB
    • SQL ROW_NUMBER
    • SQL Server Replace
    • SQL Ranking Function
    • SQL Server Permission
  • T-SQL
    • T-SQL pivot
    • T-SQL Formatter
    • T-SQL TRY CATCH
    • T-SQL CTE
    • T-SQL CASE
    • T-SQL DATEPART
    • T-SQL Date Format
    • T-SQL ROUND
    • T-SQL Loop
    • T-SQL IIF
    • T-SQL Union
    • T-SQL CREATE TABLE
    • T-SQL INSERT
    • T-SQL Stuff
    • T-SQL ISNULL
    • T-SQL ADD Column
    • T-SQL DATEDIFF
  • Joins
    • Join Query in SQL
    • Types of Joins in SQL
    • Types of Joins in SQL Server
    • SQL Inner Join
    • SQL Join Two Tables
    • SQL Delete Join
    • SQL Left Join
    • LEFT OUTER JOIN in SQL
    • SQL Right Join
    • SQL Cross Join
    • SQL Outer Join
    • SQL Full Join
    • SQL Self Join
    • Natural Join SQL
    • SQL Multiple Join
  • Advanced
    • MDF File in SQL Server
    • SQL Aliases
    • SQL Hosting
    • SQL Auto Increment
    • SQL Injection
    • SQL Wildcards
    • SQL Check
    • SQL Indexes
    • Select Distinct
    • SQL BETWEEN
    • SQLPlus spool
    • SQL Create Table
    • SQL Schema
    • Comparison Operators in SQL
    • SQL_plus
    • SQL Formatter
    • SQL LEFT INNER JOIN
    • SQL Plus Command
    • SQLPlus not found
    • SQL Injection Attack
    • Aggregate Functions in SQL
    • SQL REVOKE
    • SQL Select Distinct Count
    • IF ELSE Statement in SQL
    • SQL CASE Statement
    • SQL While Loop
    • SQL BIGINT
    • SQL Crosstab
    • SQL Wildcard Character
    • SQL INSTR()
    • SQL now
    • SQL synonyms
    • SQLite?export to csv
    • What is Procedure in SQL
    • Stored Procedure in SQL?
    • SQL Server Constraints
    • SQL DELETE ROW
    • Column in SQL
    • Table in SQL
    • SQL Virtual Table
    • SQL Merge Two Tables
    • SQL Table Partitioning
    • SQL Temporary Table
    • SQL Clone Table
    • SQL Rename Table
    • SQL LOCK TABLE
    • SQL Clear Table
    • SQL DESCRIBE TABLE
    • SQL Mapping
    • Cursors in SQL
    • AND in SQL
    • Wildcard in SQL
    • SQL FETCH NEXT
    • SQL Views
    • SQL Delete View
    • Triggers in SQL
    • SQL UPDATE Trigger
    • SQL AFTER UPDATE Trigger
    • SQL Update Statement
    • SQL DROP TRIGGER
    • SQL DROP Table
    • Types of SQL Views
    • SQL Port
    • SQL Clustered Index
    • SQL COMMIT
    • Distinct Keyword in SQL
    • PARTITION BY in SQL
    • SQL Set Operators
    • SQL UNION ALL
    • Metadata in SQL
    • SQL Bulk Insert
    • Array in SQL
    • SQL REGEXP
    • JSON in SQL
    • SQL For loop
    • EXPLAIN in SQL
    • ROLLUP in SQL
    • Escape Character SQL
    • SQL Cluster
    • SQL Backup
    • SQL Pattern Matching
    • SQL Users
    • ISNULL SQL Server
    • SQL pivot
    • SQL Import CSV
    • SQL if then else
    • SQL ignore-case
    • SQL Matches
    • SQL Search String
    • SQL Column Alias
    • SQL extensions
    • SQL Substring Function
    • Charindex SQL
  • SqlAlchemy
    • What is SQLAlchemy
    • SqlAlchemy ORM
    • SQLAlchemy count
    • SQLAlchemy update object
    • SQLAlchemy pip
    • SQLAlchemy Connection
    • SQLAlchemy Transaction
    • SQLAlchemy Metadata
    • SQLAlchemy Raw SQL
    • SQLAlchemy Filter in List
    • SQLAlchemy Alias
    • SQLAlchemy unique
    • SQLAlchemy JSONB
    • SQLAlchemy Async
    • SQLAlchemy Types
    • SQLAlchemy Many to Many
    • SQLAlchemy Example
    • SQLAlchemy Model
    • SQLAlchemy Data Types
    • SQLAlchemy Filter
    • SQLAlchemy SQLite
    • SQLAlchemy DateTime
    • SQLAlchemy create_engine
    • SQLAlchemy Delete
    • SQLAlchemy Migrations
  • NoSQL
    • NoSQL Databases List
    • NoSQL Data Modeling
    • Types of NoSQL Databases
    • NoSQL Injection
    • NoSQL vs SQL Databases
    • NoSQL Use Cases
    • NoSQL Key Value
  • Interview Questions
    • SQL Interview Questions
    • Advance SQL Interview Questions
    • SQL Joins Interview Questions
    • SQL Server Interview Questions
    • SQL Current Month

SQL Super Key

SQL Super Key

Introduction to SQL Super Key

The following article provides an outline for SQL Super Key. Super Key in relational databases is an attribute or a set of attributes that uniquely identifies a row or a record in the database table. By attribute, we mean a field or column in the table. There can be more than one super key in the database and it can also be NULL. Super key can be considered similar to super set in relational algebra.

Example:

Start Your Free Data Science Course

Hadoop, Data Science, Statistics & others

Consider a relation that has A, B, C, D, E, F as attributes.

R = {A, B, C, D, E, F}

Now, consider the following functional dependencies.

Functional Dependencies Super Key
A → B, C No
AB → C, D, E, F Yes
CD → A, B, F No
D → E, F No
CF → ABDE Yes

Out if the given functional dependencies, AB, CF are super keys because they can determine all the attributes in the relation.

A relation with n attributes can have a maximum of 2^n super keys. Newbies to relational databases often get confused between candidate key and super key. Candidate key is a subset of super key. It is the minimal key that determines all other attributes in the relation.

For illustration, consider a relation R = {A, B, C, D} and functional dependencies as A→C and B → D. Here, A and B alone cannot determine all the attributes in the relation but when we club A and B together, we are able to determine all the attributes. Hence, AB is a super key. It is minimal also because A and B alone are not super keys. Ergo, AB qualifies for candidate key too. Now you must be wondering what’s the difference between a candidate key and a primary key then. Both the keys uniquely identify a record but a primary key cannot have NULL fields but a candidate key can.

Note: All candidate keys are super keys but not vice versa. Both candidate and super keys can have NULL attributes.

Examples of SQL Super Key

Given below are the examples of SQL Super Key:

Example #1

In order to further illustrate Super Keys in relational databases, let us take help of a dummy table called “student_record”.

Here is the CREATE TABLE statement for the “student_record” table.

Code:

CREATE TABLE student_record (
id INT NOT NULL,
name CHARACTER VARYING (50) NOT NULL,
gender CHARACTER VARYING (50) NOT NULL,
phone CHARACTER VARYING (50) NOT NULL,
state CHARACTER VARYING (50) NOT NULL,
class INT
);

The table has been successfully created. The next task is to insert a few records in it to work with. You may use the given INSERT statement for this purpose.

Code:

INSERT INTO student_record(
id, name, gender, phone, state, class)
VALUES (1,'Rohit','M','989898989','MH',1),
(2,'Indira','F','942505001','MP',2),
(3,'Rohit','M','888888989','KA',1),
(4,'Priya','F','989898989','MH',1),
(5,'Steve','M','789007890','KA',2),
(6,'Priya','F','544554451','MP',2);

The command executed successfully and all the 6 records have been inserted in the table. Let’s have a look at the table using a SELECT statement.

Code:

SELECT *
FROM student_record;

Output:

SQL Super Key 1

Now let’s try to see and find super keys based on the above mentioned table.

  • {id}
  • {id, name}
  • {id,gender}
  • {id,phone}
  • {id,state}
  • {id,class}
  • {name,phone}
  • {name,state}
  • {gender,phone}
  • {id,name,gender}
  • {id,name,phone}
  • {id, name,state}
  • {id,name,class}
  • {id,gender,phone}
  • {id,gender,state}
  • {id,gender,class}
  • {id,state,class}
  • {name,phone,gender}
  • {name,gender,state}
  • .
  • .
  • .
  • {id,name,gender,phone.state,class}

All of the above mentioned and more attribute sets can be super keys provided that they uniquely determine a record. For example consider, {name, phone} key. The attributes name and phone number individually cannot determine all other attributes in the relation. But when they are clubbed together, they uniquely identify a record in the student_record table. Since, name and phone number in themselves are not super keys, {name, phone} key qualifies to be a candidate key as well in this case.

One good methodology to find super keys, which we personally found useful is listing all the possible sets of attributes and then eliminating the ones which do not determine all the attributes in the set.

Lets see one more example to illustrate it more.

Example #2

In this example we will illustrate super keys with the help of the “student_list” table.

Code:

CREATE TABLE student_list(
student_name VARCHAR(50),
class VARCHAR(50),
Subject VARCHAR(50)
);
INSERT INTO student_list(
student_name, class, subject)
VALUES ('Rohan','V','Maths'),
('Rohan','VI','Maths'),
('Steve','VI','Maths'),
('Peter','II','Science');

The data in student_list table looks something as follows :

Code:

SELECT * FROM student_list;

Output:

SQL Super Key 2

Step 1: List all possible sets of attributes.

  • {}
  • {student_name}
  • {class}
  • {subject}
  • {student_name, class}
  • {student_name,subject}
  • {class, subject}
  • {student_name, class, subject}

Step 2: Eliminate sets which do not determine all the attributes in the table/relation.

  • {student_name, class} Super Key, Candidate Key
  • {student_name, class, subject} Super Key

Here, all other sets, for example, {student_name,subject} does not uniquely determine a row. Hence, they are not super keys.

Conclusion

In this article we saw about super keys. They are a set of one or more attributes that uniquely determines a record in the relational database table.

Recommended Articles

We hope that this EDUCBA information on “SQL Super Key” was beneficial to you. You can view EDUCBA’s recommended articles for more information.

  1. SQL UNION ALL
  2. SQL Window Functions
  3. SQL DECODE()
  4. SQL SELECT DISTINCT
Popular Course in this category
JDBC Training (6 Courses, 7+ Projects)
  6 Online Courses |  7 Hands-on Projects |  37+ Hours |  Verifiable Certificate of Completion
4.5
Price

View Course

Related Courses

PHP Training (5 Courses, 3 Project)4.9
Windows 10 Training (4 Courses, 4+ Projects)4.8
SQL Training Program (10 Courses, 8+ Projects)4.7
PL SQL Training (4 Courses, 2+ Projects)4.7
Oracle Training (17 Courses, 8+ Projects)4.7
Primary Sidebar
Footer
About Us
  • Blog
  • Who is EDUCBA?
  • Sign Up
  • Live Classes
  • Corporate Training
  • Certificate from Top Institutions
  • Contact Us
  • Verifiable Certificate
  • Reviews
  • Terms and Conditions
  • Privacy Policy
  •  
Apps
  • iPhone & iPad
  • Android
Resources
  • Free Courses
  • Database Management
  • Machine Learning
  • All Tutorials
Certification Courses
  • All Courses
  • Data Science Course - All in One Bundle
  • Machine Learning Course
  • Hadoop Certification Training
  • Cloud Computing Training Course
  • R Programming Course
  • AWS Training Course
  • SAS Training Course

ISO 10004:2018 & ISO 9001:2015 Certified

© 2023 - EDUCBA. ALL RIGHTS RESERVED. THE CERTIFICATION NAMES ARE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS.

EDUCBA
Free Data Science Course

Hadoop, Data Science, Statistics & others

By continuing above step, you agree to our Terms of Use and Privacy Policy.
*Please provide your correct email id. Login details for this Free course will be emailed to you
EDUCBA

*Please provide your correct email id. Login details for this Free course will be emailed to you

Let’s Get Started

By signing up, you agree to our Terms of Use and Privacy Policy.

EDUCBA

*Please provide your correct email id. Login details for this Free course will be emailed to you
EDUCBA

*Please provide your correct email id. Login details for this Free course will be emailed to you
EDUCBA Login

Forgot Password?

By signing up, you agree to our Terms of Use and Privacy Policy.

This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy. By closing this banner, scrolling this page, clicking a link or continuing to browse otherwise, you agree to our Privacy Policy

Loading . . .
Quiz
Question:

Answer:

Quiz Result
Total QuestionsCorrect AnswersWrong AnswersPercentage

Explore 1000+ varieties of Mock tests View more