Lec-13: Super key in DBMS in HINDI | ये Question Competition Exams में अक्सर पूछा गया है
Understanding the Concept of Super Keys
Introduction to Super Keys
- The video introduces the concept of super keys, requested by students for clarity on this topic.
- A super key is defined as a combination of attributes that can uniquely identify two tuples in a table.
Candidate Key vs. Super Key
- The candidate key is emphasized as a crucial concept in DBMS, which uniquely identifies tuples.
- An example is provided using a student table with attributes: roll number, name, and age; where roll number serves as the candidate key.
- If additional attributes (name or age) are added to the candidate key (roll number), it becomes a super key.
Characteristics of Super Keys
- A candidate key is minimal; adding any attribute to it results in a super key.
- Not all combinations of attributes form a super key; at least one candidate key must be present.
Calculating Super Keys
Power Set Concept
- The video discusses numerical questions regarding how many super keys are possible given N attributes and one candidate key (A1).
- It explains the power set concept, where each attribute has two choices: included or not included.
Total Number of Super Keys
- If A1 is mandatory in every subset due to being a candidate key, then there are 2^(N - 1) possible combinations for other attributes.
Multiple Candidate Keys Scenario
Two Candidate Keys
- When both A1 and A2 are considered as candidate keys, each contributes 2^(N - 1).
Accounting for Common Sets
- The total possibilities from both candidates need adjustment for overlapping sets due to commutative properties between A1 and A2.
Final Calculation
Understanding Super Keys and Candidate Keys
Concept of Super Key
- The concept of a super key is straightforward, yet it often confuses students when presented in exam questions like those in UGC NET and GATE.
- A super key can be derived from candidate keys; for instance, if A1 and A2 are part of a composite candidate key, they can generate multiple combinations.
Combinations of Candidate Keys
- When considering two candidate keys (A3 and A4), the number of possible super keys remains consistent at 2^n - 2. This formula applies to any combination of elements within the set.
- It’s important to note that many candidate keys may share common super keys, necessitating adjustments in calculations to avoid double counting.
Calculation Insights
- The total number of unique super keys must account for overlaps among different candidate keys, which could lead to redundancy in the final count.