21. | Given relations r(w, x) and s(y, z), the result of SELECT DISTINCT w, x FROM r, s is guaranteed to be same as r, provided |
Discuss |
Answer: (a).r has no duplicates and s is non-empty
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22. | In SQL, relations can contain null values, and comparisons with null values are treated as unknown. Suppose all comparisons with a null value are treated as false. Which of the following pairs is not equivalent? |
Discuss |
Answer: (c).x < 5 AND not (x = 5)
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23. | Consider the following three table to store student enrollements in different courses. Student(EnrollNo, Name) Course(CourseID, Name) EnrollMents(EnrollNo, CourseID) (EnrollNo,CourseID are primary keys) What does the following query do? SELECT S.Name FROM Student S, Course C, Enrollments E WHERE S.EnrollNo = E.EnrollNo AND C.Name = "DBMS" AND E.CourseID = C.CourseID AND S.EnrollNo IN (SELECT S2.EnrollNo FROM Student S2, Course C2, Enrollments E2 WHERE S2.EnrollNo = E2.EnrollNo AND E2.CourseID = C2.CourseID C2.Name = "OS") |
Discuss |
Answer: (b).Name of all students who are enrolled in "DBMS" and "OS"
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24. | Consider the following Employee table ID salary DeptName 1 10000 EC 2 40000 EC 3 30000 CS 4 40000 ME 5 50000 ME 6 60000 ME 7 70000 CS How many rows are there in the result of following query? SELECT E.ID FROM Employee E WHERE EXISTS (SELECT E2.salary FROM Employee E2 WHERE E2.DeptName = 'CS' AND E.salary > E2.salary) |
Discuss |
Answer: (c).5
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25. | Select operation in SQL is equivalent to |
Discuss |
Answer: (d).the projection operation in relational algebra, except that select in SQL retains duplicates
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26. | Consider the following relation Cinema (theater, address, capacity) Which of the following options will be needed at the end of the SQL query SELECT P1. address FROM Cinema P1 Such that it always finds the addresses of theaters with maximum capacity? |
Discuss |
Answer: (a).WHERE P1. Capacity> = All (select P2. Capacity from Cinema P2)
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27. | A company maintains records of sales made by its salespersons and pays them commission based on each individual's total sales made in a year. This data is maintained in a table with following schema: salesinfo = (salespersonid, totalsales, commission) In a certain year, due to better business results, the company decides to further reward its salespersons by enhancing the commission paid to them as per the following formula: If commission < = 50000, enhance it by 2% If 50000 < commission < = 100000, enhance it by 4% If commission > 100000, enhance it by 6% The IT staff has written three different SQL scripts to calculate enhancement for each slab, each of these scripts is to run as a separate transaction as follows: T1 Update salesinfo Set commission = commission * 1.02 Where commission < = 50000; T2 Update salesinfo Set commission = commission * 1.04 Where commission > 50000 and commission is < = 100000; T3 Update salesinfo Set commission = commission * 1.06 Where commission > 100000; Which of the following options of running these transactions will update the commission of all salespersons correctly? |
Discuss |
Answer: (d).Execute T3 followed by T2 followed by T1
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28. | A table 'student' with schema (roll, name, hostel, marks), and another table 'hobby' with schema (roll, hobbyname) contains records as shown below: Table: Student ROLL NAME HOSTEL MARKS 1798 Manoj Rathod 7 95 2154 Soumic Banerjee 5 68 2369 Gumma Reddy 7 86 2581 Pradeep Pendse 6 92 2643 Suhas Kulkarni 5 78 2711 Nitin Kadam 8 72 2872 Kiran Vora 5 92 2926 Manoj Kunkalikar 5 94 2959 Hemant Karkhanis 7 88 3125 Rajesh Doshi 5 82 Table: hobby ROLL HOBBYNAME 1798 chess 1798 music 2154 music 2369 swimming 2581 cricket 2643 chess 2643 hockey 2711 volleyball 2872 football 2926 cricket 2959 photography 3125 music 3125 chess The following SQL query is executed on the above tables: select hostel from student natural join hobby where marks > = 75 and roll between 2000 and 3000; Relations S and H with the same schema as those of these two tables respectively contain the same information as tuples. A new relation S’ is obtained by the following relational algebra operation: S’ = ∏hostel ((σs.roll = H.roll (σmarks > 75 and roll > 2000 and roll < 3000 (S)) X (H)) The difference between the number of rows output by the SQL statement and the number of tuples in S’ is |
Discuss |
Answer: (b).4
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29. | In an inventory management system implemented at a trading corporation, there are several tables designed to hold all the information. Amongst these, the following two tables hold information on which items are supplied by which suppliers, and which warehouse keeps which items along with the stock-level of these items. Supply = (supplierid, itemcode) Inventory = (itemcode, warehouse, stocklevel) For a specific information required by the management, following SQL query has been written Select distinct STMP.supplierid From Supply as STMP Where not unique (Select ITMP.supplierid From Inventory, Supply as ITMP Where STMP.supplierid = ITMP.supplierid And ITMP.itemcode = Inventory.itemcode And Inventory.warehouse = 'Nagpur'); For the warehouse at Nagpur, this query will find all suppliers who |
Discuss |
Answer: (d).supply two or more items
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30. | Consider the relations r1(P, Q, R) and r2(R, S, T) with primary keys P and R respectively. The relation r1 contains 2000 tuples and r2 contains 2500 tuples. The maximum size of the join r1⋈ r2 is : |
Discuss |
Answer: (a).2000
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