Question
What are Keys in a relational database? Differentiate among the following with suitable
examples. (4 Marks)
Candidate Key
Super Key
Primary Key
Alternate Key
d. Explain Conflict Serializability.
Construct a precedence graph for a suitable schedule involving two transactions and determine
whether the schedule is conflict serializable.
Answer :
Word Count : 1452
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Skip in 10
In a relational database, a key is an attribute or a combination of attributes used to uniquely identify a tuple (row) in a relation (table). Keys are fundamental to the design of a relational database because they help maintain data integrity, prevent duplicate records, establish relationships between tables, and support efficient retrieval of data. Different types of keys are used depending on their purpose and properties. The important keys in a relational database include super key, candidate key, primary key, and alternate key. Consider a relation STUDENT with the following attributes: STUDENT(RollNo, Name, Email, Course, Phone) Suppose RollNo and Email are both unique for every student. A possible set of records may be: | RollNo | Name | Email | Course | Phone | | ------ | ---- | --------------------------------------- | ------ | ---------- | | 101 | Ravi | [ravi@gmail.com](mailto:ravi@gmail.com) | BCA | 9876543210 | | 102 | Neha | [neha@gmail.com](mailto:neha@gmail.com) | BCA | 9876543211 | | 103 | Aman | [aman@gmail.com](mailto:aman@gmail.com) | BCA | 9876543212 | A super key is any set of one or more attributes that can uniquely identify each record in a relation. A super key may contain additional attributes that are not necessary for establishing uniqueness. For example, in the STUDENT relation, RollNo is a super key because every student has a different RollNo. Similarly, Email is a super key if every email address is unique. The combination (RollNo, Name) is also a super key because RollNo alone is sufficient to identify a student, even though Name is an unnecessary attribute. Likewise, (RollNo, Email) is a super key. Thus, a relation can have many super keys. A candidate key is a minimal super key. It uniquely identifies every tuple, but none of its attributes
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