GATE CSE 1996 | Question: 27

Question

A library relational database system uses the following schema

• USERS (User#, User Name, Home Town)
• BOOKS (Book#, Book Title, Author Name)
• ISSUED (Book#, User#, Date)

Explain in one English sentence, what each of the following relational algebra queries is designed to determine

1.  $\sigma_{ \text{User#}=6}\left(\pi_{\text{User#, Book Title}}\left(\left(\text{USERS} \bowtie \text{ISSUED}\right) \bowtie \text{BOOKS}\right)\right)$
2.  $\pi_{\text{Author Name}}\left(\text{BOOKS} \bowtie \sigma_{\text{Home Town=Delhi}} \left(\text{USERS} \bowtie \text{ISSUED}\right)\right)$

Answer 1

1. Select the (user# and) titles of the books issued to User# 6
2. Select author names of the books issued to users whose home town is Delhi

Answer 2

(a) select all the book title which are issued by user id =6

 

(b) select all the author name whose book are issued by user belongs to home town delhi