Recent questions tagged databases - GATE CSE Doubts

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Self Doubt: Adding attributes/relations to BCNF to convert it into dependency preserving

asked 2 days ago in Databases by shashin (1.2k points) | 13 views

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Self Doubt: Previous GO DBMS
Query 1 is right and query 2 is wrong right? Query 2 returns SID who has NOT supplied every red part right?

asked 3 days ago in Databases by Debapaul (615 points) | 13 views

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SELF DOUBT: TAKEN FROM GO
Consider that the relation has only one attribute $A$.

asked 3 days ago in Databases by Debapaul (615 points) | 43 views

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Self Doubt:BCNF DBMS
Say you are given table like R(A,B,C,D,E,F)= {AB→C, BC → A, AC→ B , B → D , D→ E } Now how will you figure out how many tables are needed to decompose this function in $BCNF?$ Is there any short formula by which we can figure this out ... ; Any help will be highly appreciated, specially if there is some $formula$ by which we can do it within some seconds or such. Thank you.. :)

asked Jan 5 in Databases by Debapaul (615 points) | 16 views

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GO DOUBT: Previous
Consider the following statements. If relation R is in 3NF and every key is simple, then R is in BCNF If relation R is in 3NF and R has only one key, then R is in BCNF Both 1 and 2 are true 1 is true but 2 is false 1 is false and 2 is true Both 1 and 2 are false

asked Jan 5 in Databases by Debapaul (615 points) | 21 views

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Ace 2019 Mock 3 Q59
please explain ISA relationship and answer

asked Jan 3 in Databases by ssap09 (42 points) | 10 views

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Ace Mock Test 1 2020 Q48
please explain how to check 2PL?

asked Dec 27, 2019 in Databases by ssap09 (42 points) | 40 views

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Can someone give a good clarification on Dense index, sparse index?

asked Dec 23, 2019 in Databases by commenter commenter (31 points) | 9 views

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A statement about Superkey from korth book[dbms]
Statement: if t1 and t2 are in r and t1 != t2 then t1.K != t2.K where t1 and t2 are tuples , r relation and K is the superkey for r. simplify this statement? Is this always true? if we choose two attributes as set for superkey they may ... the tuple t1 and t2 if tuples are not equal. then how t1.K!=t2.K , is this true for every case when t1!=t2?

asked Dec 16, 2019 in Databases by shaktisingh (90 points) | 12 views

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Virtual GATE:DBMS-2020
Let S(A1A2A3A4A5) be relation which has 5000000 records .Size of each record is 200B .Size of attribute A1 is 16B.Size of pointer is 4B and size of the block is 2400 B (Assume elements are stored in sorted order of key).On the execution ... need to consider number of blocks or number of block access?? Here nothing mentioned directly, So, what should be calculation based on?

asked Dec 15, 2019 in Databases by srestha (636 points) | 23 views

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Virtual GATE: DBMS doubt
Consider the following table structure: CREATE table dept(dno number PRIMARY KEY,dname varchar2(30)); CREATE table emp(eno number PRIMARY KEY,ename varchar2(30),dno number references dept(dno) ON DELETE CASCADE ON UPDATE CASCADE); Which of the following statements ... . Delete on DEPT is always successful D. Update on EMP is always successful Isnot here C) and D) both ans?

asked Dec 15, 2019 in Databases by srestha (636 points) | 15 views

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Virtual GATE: DBMS 2020
Consider the table R(p,q,w) Q1:Select distinct p,q from R; Q2:Select p,q from R group by p,q; Will Q1 and Q2 produce same result? My confusion is, will group by eliminate duplicates?

asked Dec 15, 2019 in Databases by srestha (636 points) | 26 views

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Loop joins DBMS
Can anyone explain with some example how to calculate no of seeks in different types of joins like Block level Nested loop Join,Nested loop Join,Merge Join etc ?

asked Dec 9, 2019 in Databases by Shivateja MST (96 points) | 10 views

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DBMS doubt Calculus
In result of Tuple Relational Calculus or Domain Relational calculus is it true that duplicates are not allowed? How can this be assumed ? Anyone please clarify.

asked Dec 6, 2019 in Databases by Shivateja MST (96 points) | 6 views

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Virtual GATE-DBMS
Select the relational expression , which could possibly return following result: a c 1 2 2 3 $A)$ $\pi _{a<c}\left ( \pi _{a,c}R \right )$ $B)$ $\sigma _{a<c}\left ( \pi _{a,c}R \right )$

asked Dec 2, 2019 in Databases by srestha (636 points) | 11 views

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ACE Test Series DBMS
Anyone please reply what would be the correct Answer?

asked Nov 26, 2019 in Databases by Shivateja MST (96 points) | 9 views

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Self doubt: DBMS
Plz someone tell me In this question https://gateoverflow.in/39550/gate2016-2-22 how option D) incorrect? exclusive locks to O1,…,Ok in increasing order of their addresses. of this question saying, increasing order of address in lock, can ensure serializability, but it violates here. Moreover, why BFS is wrong?

asked Nov 24, 2019 in Databases by srestha (636 points) | 38 views

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All minimal covers
Can some one give any method to find all possible minimal covers for a set of functional dependencies?

asked Nov 18, 2019 in Databases by Shivateja MST (96 points) | 10 views

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DBMS SELF DOUBT:2020 GATE
We know all 2pl are conflict serializable, but are all conflict serializable schedules also $2PL$?

asked Nov 18, 2019 in Databases by Debapaul (615 points) | 14 views

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No of Conflict Serializable schedules
Can any one explain how to find the number of Conflict serializable schedules possible for given schedule,when more than 2 transactioms are in schedule?

asked Nov 10, 2019 in Databases by Shivateja MST (96 points) | 15 views

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Self Doubt : DBMS
Find the minimum number of tables required for each case.

asked Oct 29, 2019 in Databases by Debapaul (615 points) | 25 views

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DBMS SELF DOUBT 2020
How to read the arrow representation? does the arrow on E1 from E3 means they are in $many:1$ $total-total$ relation? And so does, E1 and E2 are in $many:many$ $partial-total$ relation?

asked Oct 29, 2019 in Databases by Debapaul (615 points) | 21 views

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Self doubt- Dbms(SQL)
https://gateoverflow.in/47/gate2012-15 One of the statement given in the question & it is true. S: Not all attributes used in the GROUP BY clause need to appear in the SELECT clause. What about them ? $\\ select\ B\\ from\ R\\ group\ by\ A\\ \\$ ... $select\ Avg(C)\\ from\ R\\ group\ by\ A\\ \\$ $select\ A\\ from\ R\\ group\ by\ (A,B)\\$

asked Oct 29, 2019 in Databases by Kushagra गुप्ता (175 points) | 11 views

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Self doubt- Dbms(RA)
Retrieve sid’s enrolled every korth course & every navathe course: $\Pi _{sidcid}Enroll/\ \Pi_{cid}(\sigma _{inst=korth\ \vee\ inst=navathe}(course))$ Note: Why there is an OR operator in the query and still the query is correct. Not able to understand, if someone can tell it would be helpful.

asked Oct 28, 2019 in Databases by Kushagra गुप्ता (175 points) | 9 views

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N ary Relation Table
“For an n-ary relationship set with an arrow on one of its edges, the primary keys of the entitysets not on the “arrow” side of the relationship set serve as the primary key for the schema.” Can anyone please explain the following statement with some example.

asked Oct 18, 2019 in Databases by Shivateja MST (96 points) | 11 views

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Diffrerence between Functional Dependency and Fully Functionally Dependency on primary Key

asked Oct 10, 2019 in Databases by HeartBleed (57 points) | 16 views

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Self Doubt Mtech Assignments.
which of the following sequences is serializable. a) $S_a=R_1(x)R_2(x)W_1(x)R_3(x)R_4(x)W_3(x)$ b) $S_b = R_1(x)W_1(x)R_2(x)W_2(x)W_3(x)W_4(x)R_5(x)$ c) $S_c=R_1(x)W_1(x)W_2(x)R_2(x)$

asked Oct 10, 2019 in Databases by `JEET (178 points) | 20 views

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Source : made easy test series DBMS
What should be the answer to this question. Also please provide the explanation for the answer.

asked Sep 21, 2019 in Databases by karanvashisht1026 (7 points) | 56 views

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Gatebook;DBMS
Consider the relation employee(name,sex,manager) with name as the key, manager gives the name of the supervisor of the employee under consideration. What does the following Tuple Relational Calculus query produce? A. Names of employees who have a female subordinate B. ... manager How to interpret this TRC expression? The y.name = e.manager =>x.sex=female part is troublesome.

asked Sep 19, 2019 in Databases by Sambhrant Maurya (335 points) | 21 views

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Gatebook; DBMS
In translating from an entity-relationship (E-R) diagram to a relational schema, one piece of E-R logic that cannot be captured by primary keys, uniques, and foreign keys is (A) the weak entity. (B) any ternary relationship. (C) mandatory participation for one-time occurrence (that is, with the arrow). (D) mandatory participation for many-time occurrence (that is, without the arrow).

asked Sep 19, 2019 in Databases by Sambhrant Maurya (335 points) | 16 views

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Gatebook:DBMS
Consider the following entity-relationship (ER) model For the following group of statements, which one does not coincide (Or not true) with the model ? (A) Each person has at most one e-mail address. (B) Each e-mail address belongs to exactly ... passport number? eg I can assign 3 passport numbers to the same person Pinkman. Passport Number Name 101 Pinkman 102 Pinkman 103 Pinkman

asked Sep 19, 2019 in Databases by Sambhrant Maurya (335 points) | 10 views

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Gatebook: DBMS
Consider the following table Mystery A B 1 null 2 4 3 5 null 6 select count() from Mystery where A not in( select B from Mystery) What is the output of this query? (A) 1 (B) 0 (C) 4 (D) 3

asked Sep 19, 2019 in Databases by Sambhrant Maurya (335 points) | 16 views

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[GATEBOOK TS] how many completely non trivial FD hold for the given instance?

asked Sep 18, 2019 in Databases by ummokkate (45 points) | 11 views

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DBMS self clearance
Can someone explain me group by and having clause in a clear way.

asked Sep 17, 2019 in Databases by Priyansh Singh (219 points) | 9 views

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Made Easy: DBMS
What is the minimum number of tables needed in the relational model? 2 3 4 5

asked Sep 14, 2019 in Databases by Sambhrant Maurya (335 points) | 62 views

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Virtual Gate:DBMS
Consider a relation R(A,B) where A is the primary key and B is a foreign key which references the same relation. Consider the following relation instance of R. A 2 3 5 7 4 3 B 4 4 2 2 5 4 Which of the following tuple to be deleted first to preserve the referential integrity constraint ... tuple (2,4) is deleted? (2,4) (5,2) (7,2) (4,5) p.s The obvious answer (5,2) is given wrong.

asked Sep 14, 2019 in Databases by Sambhrant Maurya (335 points) | 25 views

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Virtual Gate: DBMS
'A' is set of all possible schedules 'C' is set of all possible schedules that are guaranteed to produce a correct final result 'S' is the set of all serializable schedules 'P' is the set of all schedules possible under 2-phase locking protocol Which is FALSE? (A) P⊆C (B) S⊂P (C) S⊆P (D) P⊂C

asked Sep 14, 2019 in Databases by Sambhrant Maurya (335 points) | 7 views

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functional dependency
Is there any difference between lossless decomposition and join dependency or both are same. both definition has same criteria. https://en.wikipedia.org/wiki/Join_dependency https://en.wikipedia.org/wiki/Lossless-Join_Decomposition Thanks

asked Sep 13, 2019 in Databases by piyushhurpade (6 points) | 11 views

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SQL self doubt
ENo SSN 1 15 2 20 3 15 4 null 5 null Relation R SELECT SSN,count(*) FROM R GROUP BY SSN Will the output be: SSN count 15 2 20 1 null 2 SSN count 15 2 20 1 null 1 null 1 SSN count 15 2 20 1

asked Sep 12, 2019 in Databases by Sambhrant Maurya (335 points) | 12 views

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Success Gateway: DBMS
Consider the following ER diagram. Assume that there are no multivalued attributes present in any of E1,E2,R and each entity set has a key. What is the minimum number of tables required to convert this ER diagram into relations when: (i) E1 has total participation in R (ii) E2 has total participation in R (iii) Both E1 and E2 have total participation in R

asked Sep 12, 2019 in Databases by Sambhrant Maurya (335 points) | 14 views

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