MySQL + SQL · Lesson 1

Dbms Keys Explained

All Keys in One Place

This page summarizes every key type in DBMS with a single clear example.

Every Key Type

KeyOne-line Meaning
Super keyAny unique-identifying column set
Candidate keyMinimal super key
Primary keyChosen main identifier (unique, not null)
Alternate keyCandidate keys not chosen primary
Foreign keyRefers to another table's primary key
Composite keyMade of multiple columns

School Example

students(roll_no PK, admission_no UNIQUE, name)
marks(roll_no FK, subject, score, PRIMARY KEY(roll_no, subject))
marks uses a COMPOSITE primary key (roll_no + subject) and roll_no is a FOREIGN key.

Summary

  • Keys: super, candidate, primary, alternate, foreign, composite.
  • Composite keys combine columns; foreign keys link tables.
🔗

Share this topic with a friend

यह topic किसी दोस्त को भेजें

Found it useful? Send it to a classmate learning the same thing.

अच्छा लगा? जो दोस्त यही सीख रहा है, उसे भेज दीजिए।