Question

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:

π_empNo(empAge ⋈ _(age>age1) ρ_{empNo 1, age1}(empAge))

What does the above expression generate?

1. Employee numbers of only those employees whose age is the maximum.
2. Employee numbers of all employees whose age is not the minimum.
3. Employee numbers of only those employees whose age is more than the age of exactly one other employee.
4. Employee numbers of all employees whose age is the minimum.

Answer 1

Correct Answer - Option 2 : Employee numbers of all employees whose age is not the minimum.

Answer: Option 2

Explanation:

Consider the empAge(empNo, age) Table

empNo	age
100	22
101	21
102	23
103	24
104	25
105	26
200	22
201	21
202	23
203	24
204	25
205	26
206	27

We run the following Query on above Table 

IIempNo(empAge ⋈ (age>age1) ρempNo 1, age1(empAge))

We get Output Table as 

empNo
100
102
103
104
105
200
202
203
204
205
206

Hence the Output is "Employees whose age greater than at least one employee" or "Employees whose age is no minimum".