List of practice Questions

Consider the following three relations in a relational database. 

Employee(\(eId\), Name), Brand(\(bId\), bName), Own(\(eId\), \(bId\)) 

Which of the following relational algebra expressions return the set of \(eId\)'s who own all the brands?

A relation \( r(A,B) \) has 1200 tuples. 
Attribute \( A \) ranges from 6 to 20 and attribute \( B \) ranges from 1 to 20. Assume independent uniform distribution. The estimated number of tuples in \( \sigma_{(A>10)\vee(B=18)}(r) \) is \(\underline{\hspace{2cm}}\).

The following relation records the age of 500 employees of a company, where empNo (indicating the employee number) is the key:
\[ empAge(empNo, age) \] Consider the following relational algebra expression:
\[ \Pi_{empNo}\big( empAge \;\Join_{age > age_1}\; \rho_{empNo_1,\,age_1}(empAge) \big) \] What does the above expression generate?