Recent questions and answers in Databases - GATE CSE Doubts

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Made Easy Test Series, DBMS, Functional Dependencies

answered 13 hours ago in Databases by Abhisheksmile94 (193 points) | 23 views

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GATE 2001 DBMS
Suppose the adjacency relation of vertices in a graph is represented in a table Adj(X,Y). Which of the following queries cannot be expressed by a relational algebra expression of constant length? A List of all vertices adjacent to a given vertex B ... of less than three vertices D List all vertices reachable from a given vertex *Please elaborate all the solutions of this question.

asked 1 day ago in Databases by donniedarko (21 points) | 10 views

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Made Easy Test Series, DBMS, Normalization
Can anyone please explain how B) and D) are true? 2NF requires us to have no partial dependency on key for some non-key attributes. 3NF requires us to have no transitive dependency OR X->Y non trivial dependencies where either X is SK or Y are all prime attributes. Can anyone please explain how this leads to options B and D being true? Thanks.

asked 1 day ago in Databases by sankalpmittal (41 points) | 8 views

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Made easy test series
how? can u plese draw them?

asked 3 days ago in Databases by Salla shivateja (19 points) | 19 views

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ME Test Series
I have a doubt, How many rows will be returned when All values of R2.A will be Null….in this case number of rows Natural Join should give 0 rows ….what will be minimum number of rows???

answered 4 days ago in Databases by ashutoshbsathe (5 points) | 16 views

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Elmsari Fundamentals , Normalisation
Consider the universal relation A = {P,Q,R,S,T,U,V,W,X,Y,Z} and the set of functional dependencies FD's = { PQ -> R, R -> ST, Q -> U, U -> VW, S-> XY }. What is the key for A. Decompose A into 2NF and 3 NF relations

asked 6 days ago in Databases by Lucifer2440 (5 points) | 10 views

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TGA test series
Consider the following table P and Q .In table P, A is Primary key and B is foreign key referencing C in table Q with on delete Cascade.In table Q C is primary key and D is foreign key referencing A in table P with on delete Cascade.in order to delete record (2,6) from the table P.the ... 9 6 (Q C D 1 1 6 2 2 1 9 7 5 9 7 1 Last row of P is blanck by mistake it is added..ignore it)

answered 6 days ago in Databases by Abhisheksmile94 (193 points) | 27 views

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Joins in Relational Algebra (Self Doubt) while reading Elmasri Navathe

asked 6 days ago in Databases by shubhojit1412 (5 points) | 15 views

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Database management systems
If a schedule is given and it is asked whether the given schedule is serializable or not, is it asking about conflict serializability or view serializability? And when it is asked about the precedence graph, is it about the precedence graph that we draw to check conflict serializability or the one for view serializability?

asked 6 days ago in Databases by Abhilash Behera (5 points) | 10 views

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GATEBOOK TS (DB)
$Given\ statement:$ Wound - wait and wait - die algorithms are pessimistic deadlock avoidance algorithms and can cause more transaction aborts than needed. My doubt: Yes I totally agree that they are pessimistic deadlock avoidance algorithms but how can they directly ... of transactions that will be aborted in the wait-die method. This should be the right statement. Is it not ?

answered Jan 8 in Databases by StoneHeart (735 points) | 174 views

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Ace test series
Ace say answer is C….but i find it incorrect...Please confirm if A is valid or C is valid answer

answered Jan 8 in Databases by Abhisheksmile94 (193 points) | 25 views

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FULL OUTER JOIN
Can anyone please explain how minimum number of tuples in case of Full Outer Join is max(m,n) using a proper example?

answered Jan 8 in Databases by Abhisheksmile94 (193 points) | 12 views

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Applied test Series DBMS
Consider the following relation R with attributes as A, B, C, D, and E with functional dependencies (FDs) as marked below: For example, the arrow coming from attribute B is towards the attribute C, therefore, the FD will be B -> C. Which of the ... -prime attributes. Therefore, the relation R is neither in 2NF nor in 3NF. Hence, the correct options are (iii), and (iv).

answered Jan 7 in Databases by Sgr007 (21 points) | 39 views

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The database system then writes out enough information to disk

asked Jan 7 in Databases by Tara22 (13 points) | 12 views

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Gate applied course
If an E-R model says E having at least one multi-valued attribute is converted into relational model say R then what will be the number of simple candidate key possible in R if E has only single attribute as candidate key? A) 0 B) exactly 1 c) more than 1 d) can’t say

asked Jan 6 in Databases by Gopichandankem (5 points) | 21 views

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why we cannot undo a committed transaction
We have the log file that has all information to undo this committed transaction, so why it says we cannot? once a transaction has committed we cannot undo its effect by aborting it.

asked Jan 6 in Databases by Tara22 (13 points) | 17 views

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NPTEL Assignment Question
S1 : r1(x),r2(x),w2(x),r3(x),w1(x), w2(y),r3(y),w3(x) S2 : r2(x),r1(x),w1(x),w2(x),w2(y),r3(x),w3(x),r3(y) The answer Says Both of them are view equivalent. My Doubt is that there Initial Read Don't ... first and In S2 T2 is reding it first. Same doubt as in this question https://csedoubts.gateoverflow.in/6351/nptel-view-serialisability but it is unclear even in this.

answered Jan 4 in Databases by Abhisheksmile94 (193 points) | 23 views

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THE GATE ACADEMY ts
Does B+ tree support random access?

answered Jan 3 in Databases by Abhisheksmile94 (193 points) | 32 views

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Allowed Functional Dependencies in DBMS
Why functional dependencies of the from Non-Prime → Prime, are not allowed, I had encountered this logic in Made Easy Test Series and was unable to imagine a contradiction for this statement. Explanation with example would be appreciated.

asked Jan 1 in Databases by ronak.ladhar (5 points) | 13 views

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3 answers

ACE TEST SERIES: DBMS
The number of serial schedules which are view equal to schedule(s) but not conflict equal to schedule(s) are ________.

answered Jan 1 in Databases by Karan Negi (5 points) | 95 views

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Made Easy Test series Database Q1
Assume S is a schedule that has both read and write operations with different transactions and different data variables. Also assume all the operations are atomic in nature. Which of the following are true? S with no dirty read then S is ... . S with no dirty read then S is conflict serializable schedule S with no dirty read then S is strict serializable.

answered Dec 30, 2020 in Databases by anurags228 (23 points) | 38 views

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Self doubt - 2 Phase Locking
Does 2 Phase Locking Protocol ensures a Schedule as recoverable?

asked Dec 30, 2020 in Databases by mani312 (5 points) | 9 views

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restore/recover
What's the difference between recover' and restore'? can we use recover' instead of restore' here? If the transaction does not complete its execution, the database system restores the old values from the log to make it appear as though the ... specifically, it is handled by a component of the database called the recovery system, which we describe in detail in Chapter 19.

asked Dec 28, 2020 in Databases by Tara22 (13 points) | 19 views

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GATE 2017 SET 1 Question 42
What is “Timestamp wrap around” in Timestamp Ordering Concurrency Control?

asked Dec 28, 2020 in Databases by Praddyumn (5 points) | 12 views

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Self_doubts#
Lets consider a relation R(A,B,C,D) following are the functional dependencies on the relation R. AB ---> CD BC ---> AD AC ---> D My doubt is whether the functional dependency AC --->D is in 2NF or not? Here {AB, BC} are Candidate Keys.

answered Dec 27, 2020 in Databases by Sahil91 (645 points) | 14 views

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Gate Previous Year
R(A,B,C,D) is a relation. Which of the following does not have a lossless join, dependency preserving BCNF decomposition? (a) A→ B, B → CD (b) A → B, B→C, C→ D (c) AB→ C, C→ AD (d) A → BCD

asked Dec 26, 2020 in Databases by Rishav Chetan (9 points) | 6 views

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GATE2008-82 Video Solution
Consider the following $ER$ diagram The minimum number of tables needed to represent $M$, $N$, $P$, $R1$, $R2$ is $2$ $3$ $4$ $5$

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 7 views

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GATE2005-75 Video Solution
Let $E_1$ and $E_2$ be two entities in an $E/R$ diagram with simple-valued attributes. $R_1$ and $R_2$ are two relationships between $E_1$ and $E_2$, where $R_1$ is one-to-many and $R_2$ is many-to-many. $R_1$ and $R_2$ do not have ... of their own. What is the minimum number of tables required to represent this situation in the relational model? $2$ $3$ $4$ $5$

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 5 views

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GATE2004-IT-73 Video Solution
Consider the following entity relationship diagram $(ERD)$, where two entities $E1$ and $E2$ have a relation $R$ of cardinality 1:m. The attributes of $E1$ are $A11$, $A12$ and $A13$ where $A11$ is the key attribute. The attributes of $E2$ are $A21$ ... normal form ($3NF$) is designed from the above $ERD$. The number of tables in the database is $2$ $3$ $5$ $4$

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 9 views

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GATE2015-1-41 Video Solution
Consider an Entity-Relationship $(ER)$ model in which entity sets E$_{1}$ and E$_{2}$ are connected by an m:n relationship R$_{12}$. E$_{1}$ and E$_{3}$ are connected by a 1 : n (1 on the side of E$_{1}$ ... relational model is derived from the above $ER$ model, then the minimum number of relations that would be generated if all relation are in $3NF$ is________________.

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 9 views

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GATE1998-2.19 Video Solution
Which of the following query transformations (i.e., replacing the l.h.s. expression by the r.h.s expression) is incorrect? R1 and R2 are relations, C1 and C2 are selection conditions and A1 and A2 are attributes of R1. A. ... $\pi_{A_1} \left(\sigma_{C_1}\left(R_1\right)\right) \to \sigma_{C_1} \left(\pi_{A_1}\left(R_1\right)\right)$

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 13 views

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GATE1999-1.18, ISRO2016-53 Video Solution
Consider the join of a relation $R$ with a relation $S$. If $R$ has $m$ tuples and $S$ has $n$ tuples then the maximum and minimum sizes of the join respectively are $m+n$ and $0$ $mn$ and $0$ $m+n$ and $|m-n|$ $mn$ and $m+n$

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 10 views

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GATE2007-IT-65 Video Solution
Consider a selection of the form $\sigma_{A\leq 100} (r)$, where $r$ is a relation with $1000$ tuples. Assume that the attribute values for $A$ among the tuples are uniformly distributed in the interval $[0, 500].$ Which one of the following options is the best estimate of the number of tuples returned by the given selection query ? $50$ $100$ $150$ $200$

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 8 views

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GATE2004-13 Video Solution
Let $R_1 \left(\underline{A}, B, C\right)$ and $R_2\left(\underline{D}, E \right) $ be two relation schema, where the primary keys are shown underlined, and let C be a foreign key in $R_1$ referring to $R_2$. Suppose there is no violation of the above referential ... $\Pi_D \left(r_1 \bowtie_{C \neq D}r_2\right)$ $\Pi_C \left(r_1 \bowtie_{C = D}r_2\right)$

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 8 views

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GATE2004-51 Video Solution
Consider the relation Student (name, sex, marks), where the primary key is shown underlined, pertaining to students in a class that has at least one boy and one girl. What does the following relational algebra expression produce? (Note: $\rho$ ... of girl students with marks not less than some boy student names of girl students with more marks than all the boy students

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 13 views

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GATE2007-59 Video Solution
Information about a collection of students is given by the relation $\text{studInfo(}\underline{\text{studId}},\text{ name, sex)}$. The relation $\text{enroll(}{\text{studId}},{\text{ courseId}})$ gives which student has enrolled for ( ... Courses in which a proper subset of female students are enrolled. Courses in which only male students are enrolled. None of the above

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 9 views

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consistence constraints
The text below is from Silberschatz book. Can you please explain how consistence constraints can be verified by integrity constraints? Ensuring consistency for an individual transaction is the responsibility of the application programmer who codes the transaction. This task may be facilitated by automatic testing of integrity constraints, as we discussed in Section 4.4.

asked Dec 26, 2020 in Databases by Tara22 (13 points) | 6 views

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GATE2014-3-30 Video Solution
Consider the relational schema given below, where eId of the relation dependent is a foreign key referring to empId of the relation employee. Assume that every employee has at least one associated dependent in the dependent relation. employee (empId, ... is greater than that of some dependent. all dependents. some of his/her dependents. all of his/her dependents.

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 8 views

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GATE2008-68 Video Solution
Let R and S be two relations with the following schema $R(\underline{P,Q}, R1, R2, R3)$ $S(\underline{P,Q}, S1, S2)$ where $\left\{P, Q\right\}$ is the key for both schemas. Which of the following queries are equivalent? $\Pi_P \left(R \bowtie S\right)$ ... Only I and II Only I and III Only I, II and III Only I, III and IV

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 9 views

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GATE2012-43 Video Solution
Suppose $R_{1} (\underline{A}, B)$ and $R_{2} (\underline{C}, D) $ are two relation schemas. Let $r_{1}$ and $r_{2}$ be the corresponding relation instances. $B$ is a foreign key that refers to $C$ in $R_{2}$. If data in $r_{1}$ and $r_{2}$ satisfy referential ... $\prod_{B}(r_{1}) = \prod _{C}(r_{2})$ $\prod_{B}(r_{1}) - \prod _{C}(r_{2}) \neq \varnothing$

answered Dec 26, 2020 in Databases by amitkhurana512 (35 points) | 9 views

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