Databases Test ...

Which of the following expressions should be used to find the name and address of all students who study in the ‘Science’ department?

The relational schemas are:

Student(Sno, name, address, age)

Department(Dno, Dname, Snumber, building)

Consider a database that has the relation schema Random(A, B, C). An instance of the schema Random is as given below.

Tuple calculus expression for the above instance is given as  {t.B | t ϵ r ∧ (t[A] = 10  ∧ t[C] = 7)}

What is the sum of the elements in the output row of the given expression?

Which of the following has the same expressive power with regard to relational query language?

(a) Relational algebra and Domain relational calculus

(b) Relational algebra and Tuple relational calculus

(c) Relational algebra and Domain relational calculus restricted to safe expression

(d) Relational algebra and Tuple relational calculus restricted to safe expression

Let the database has two relations P(a, b) and Q(m, a, n) in which a is the primary key of the relation P and m is the primary of the relation Q. Instance of P has 70 Tuples and Instance of Q has 42. What is the maximum number of rows in the new instance produced by P ⨝ Q? (⨝ is natural join)

Consider the following relation Demo:

The number of tuples returned for the query \(Π_{salary} (Demo)-Π_{Demo.salary} (σ_{Demo.salary<d.salary} (Demo×ρ_d (Demo)))\) is ____.

Let the two-relation schema be R (A, B,) and S (A, B). which of the following is equivalent to R ∩ S

I. R – (R – S)

II. S – (S – R)

III. R U S – ((S – R) – (R – S))

IV. ((R U S – (S – R)) – (R – S)

Consider the following relational schema for Employees (SME):

The following query is made on the database.

D1 → \({{\rm{\Pi }}_{Test \;ID,\; TestSeries\;Name}}\left( {{\sigma _{SME\;age > 23 \wedge SME\; age < 26}}\left( {SME} \right)} \right)\)

D2 → \({{\rm{\Pi }}_{Test\;ID,TestSeries\;Name}}\left( {{\sigma _{Ratings > 9.1 \wedge Ratings < 9.4}}\left( {SME} \right)} \right)\)

D → D2 - D1

The total no. of rows in D is ______. 

Consider the following relation schema

Sailors(sid, sname, rating, age)

Reserve(sid, bid, day)

Boats(bid, bname, color)

What is the equivalent of following relational algebra query in SQL query.

π_sname((σcolor= ‘red’Boats) ⨝ Reserves ⨝ Sailors)  

Consider the following relations:

course:

teaches:

instructor:

What is the number of tuples returned when the following query is executed:

\(Π_{name,title} (σ_{deptname="Computer Science"}(instructor⋈teaches⋈course)) \)

Consider a database that has the relation schema CR(StudentName. CourseName). An instance of the schema CR is as given below.

The following query is made on the above instance in Database

TEMP ← Π_{Department_Name}(σ _{Employee_Name = ''ED"} (Employee_Record))

RESULT ← Employee_Record ÷ TEMP
The number of rows in RESULT is _______.