Recent questions tagged databases - GATE CSE Doubts

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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 5 days ago in Databases by Shivateja MST (45 points) | 14 views

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

asked Oct 29 in Databases by Debapaul (214 points) | 24 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 in Databases by Debapaul (214 points) | 18 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 in Databases by Kushagra गुप्ता (102 points) | 10 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 in Databases by Kushagra गुप्ता (102 points) | 8 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 in Databases by Shivateja MST (45 points) | 9 views

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Diffrerence between Functional Dependency and Fully Functionally Dependency on primary Key

asked Oct 10 in Databases by HeartBleed (56 points) | 12 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 in Databases by `JEET (157 points) | 15 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 in Databases by karanvashisht1026 (7 points) | 52 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 in Databases by Sambhrant Maurya (277 points) | 13 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 in Databases by Sambhrant Maurya (277 points) | 8 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 in Databases by Sambhrant Maurya (277 points) | 7 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 in Databases by Sambhrant Maurya (277 points) | 13 views

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

asked Sep 18 in Databases by ummokkate (45 points) | 9 views

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

asked Sep 17 in Databases by Priyansh Singh (70 points) | 7 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 in Databases by Sambhrant Maurya (277 points) | 57 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 in Databases by Sambhrant Maurya (277 points) | 24 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 in Databases by Sambhrant Maurya (277 points) | 6 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 in Databases by piyushhurpade (6 points) | 9 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 in Databases by Sambhrant Maurya (277 points) | 11 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 in Databases by Sambhrant Maurya (277 points) | 12 views

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Self Doubt - Nested Loop Join (No. of Seeks)
What do you mean by Seek? For Natural Loop Join, we calculate No. of Seeks are (nr + br). Assume that, Relation r is called the Outer Relation and Relation s is called the Inner Relation. (ni,bj) – ni represents total no. of tuples and bj represents no. of blocks in that relation. Reference (Korth) – For Block Nested-Loop Join –

asked Sep 10 in Databases by ayushsomani (13 points) | 16 views

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Safe query expression
From this link How The last query is safe?

asked Sep 10 in Databases by Lakshman Patel RJIT (102 points) | 13 views

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Navathe DBMS Self Doubt
what does this statement means? “In TO the schedule is equivalent to the particular serial order corresponding to the order of the transaction timestamps”

asked Sep 7 in Databases by aditi19 (51 points) | 10 views

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madeeasytestseries
I In the above question whether my solution is correct ? If not can anyone please explain with an example

asked Sep 5 in Databases by Manasa.M (19 points) | 15 views

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Testbook Test Series: databases

asked Sep 1 in Databases by Alka Kasotia (7 points) | 20 views

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Definition of Non - trivial FD - DBMS Doubt
Consider the following FDs : Sid → Sname Sname → Age The above set of FD is not - non trivial. I knw da definition of non - trivial in FD is that there should be no common element between X and Y attribute sets in the FD X → Y. ... something in common that is Sname. That is why the set of FDs is not non-trivial. Is my perception towards the FDs correct ?

asked Aug 19 in Databases by user2525 (1.6k points) | 23 views

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Equivalence of Functional Dependency
Hi all. I have a slight doubt regarding checking equivalence of two given FD sets. The traditional method that I used to follow is that taking each FD from one set, and finding its closure on the other to check if one covers the another. This ... each attribute matches then it's equivalent. I am not sure if this method is correct or not. Please help. Thank you

asked Aug 3 in Databases by DukeThunders (251 points) | 8 views

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Transaction management
Do cascadeless schedule allow committed blind writes ? Cascadeless schedule: A cascadeless schedule is one where, for each pair of transactions Ti and Tj such that Tj reads a data item previously written by Ti , the commit operation of Ti appears before ... x) W(x) Commit Abort If so, then this won't be recoverable.But cascadeless schedules come under recoverable schedules .

asked Jul 1 in Databases by vk_9_1_9 (6 points) | 12 views

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Karnataka PGCET 2017
Given an attribute X, another attribute Y is dependent on it, if for a given X (A) There are many Y values (B) There is only one value of Y (C) There is one or more Y values (D) There is none or one Y values

asked Jun 24 in Databases by Prajna (15 points) | 17 views

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DBMS self doubt regarding BCNF
Hi everyone, I had a little doubt in DBMS regarding BCNF. Can we say that in a relation if all the attributes are candidate keys, the relation will be always in BCNF? Taking a relation R(A,B,C,D) with FDs like A->B,B->C,C->D,D->A. Here all the atributes are CKs. The relation is in BCNF. Can it be said for all such relations? Thanks.

asked Jun 22 in Databases by DukeThunders (251 points) | 15 views

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