SQL Keys are constraints in a database used to uniquely identify rows and establish relationships between tables. Common keys include Primary, Foreign, Candidate, Composite, Super, and Alternate Keys.

What is the difference between Primary Key and Foreign Key?

A Primary Key uniquely identifies each record in a table, while a Foreign Key is a field in one table that refers to the Primary Key in another table, creating a relationship between them.

Why are SQL Keys important?

SQL Keys ensure data integrity, avoid duplication, and maintain relationships between tables, making database design efficient and reliable.

SQL Keys Interactive Demo

🔑 SQL Keys Explorer

Key Concepts: SQL Keys help uniquely identify records in a database. Click any key type to learn more!

What are SQL Keys?
Keys uniquely identify records in a database. Click a key type to explore!

🎭 Fun Analogies

Learn with Fun: Understand database keys with real-world analogies!

🏠 Community Analogy

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Which key do you want to learn about? Select one above!

🎮 Interactive Example

Select a key type to see an interactive example...

📊 Visual SQL Keys Demonstration

👨‍🎓 Students Table Example

🗝️ StudentID (PK)	Name	Email	🔄 AadharNo (AK)	Phone
101	Jethalal	jethalal@gokuldham.com	1234-5678-9012	9876543210
102	Bhide	bhide@discipline.com	2345-6789-0123	8765432109
103	Popatlal	popat@reporter.com	3456-7890-1234	7654321098

Key Points:
🗝️ Primary Key: StudentID - Uniquely identifies each student
🔄 Alternate Key: AadharNo - Unique but not chosen as Primary
🎯 Candidate Keys: StudentID, Email, AadharNo - All can uniquely identify records

📚 Enrollment Table Example

🧩 StudentID (CK)	🧩 SubjectCode (CK)	Grade	Semester
101	MATH101	A	1
101	PHY101	B+	1
102	MATH101	A+	1

Key Points:
🧩 Composite Key: (StudentID + SubjectCode) - Together uniquely identify records
🔗 Foreign Key: StudentID - Links to Students table’s Primary Key
🦸 Super Key: (StudentID + SubjectCode + Grade) - Includes extra columns but still unique

🔗 Table Relationships Visualization

/* Students Table */
CREATE TABLE Students (
  StudentID INT PRIMARY KEY,
  Name VARCHAR(50),
  Email VARCHAR(100) UNIQUE,
  AadharNo VARCHAR(12) UNIQUE
);

/* Enrollment Table */
CREATE TABLE Enrollment (
  StudentID INT,
  SubjectCode VARCHAR(10),
  Grade VARCHAR(5),
  PRIMARY KEY (StudentID, SubjectCode),
  FOREIGN KEY (StudentID) REFERENCES Students(StudentID)
);

🔍 SQL Keys Comparison

Key Type	Definition	Properties	Fun Analogy
🗝️ Primary Key	Uniquely identifies each record	Not NULL, Unique, Only one per table	Like the head of a community—only one leader!
🔗 Foreign Key	Links a column to a Primary Key in another table	Can be NULL, Maintains referential integrity	Like a connection to a trusted friend!
🎯 Candidate Key	Any column(s) that can uniquely identify records	Multiple per table, Unique, Minimal	Like candidates eligible to lead the community!
🧩 Composite Key	Combination of two or more columns	Unique together, May not be unique individually	Like a team effort—both members needed!
🦸 Super Key	Any combination that uniquely identifies a row	May include extra columns, Not minimal	Like identifying someone with extra details!
🔄 Alternate Key	Candidate Key not chosen as Primary	Unique but not selected as Primary	Like a backup leader who didn’t get chosen!

Master SQL Keys