# Recent questions and answers in Databases 0 votes
0 answers 7 views
Let R be a relation. Which of the following comments about the relation R are correct ? R will necessarily have a composite key if R is in BCNF but not in 4NF If R is in 3NF and if every key of R is simple, then R is in BCNF If R is in BCNF and if R has at least one simple key , then R is in ... and if its every key is simple, then R is in 5NF a) 1 and 4 b) 2 and 3 c) 1, 2 and 3 d) 1, 2, 3 and 4
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0 answers 5 views
Redundancy is dangerous as it is a potentiad threat to data integrity consistency sufficiency both 1 and 2 Answer is 4 but why ?
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0 answers 7 views
I cannot understand why is option D) incorrect? Can anyone give an example of how in option D) first one can contain duplicate values and second one cannot ? Kindly help me. Thanks in advance
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1 answer 16 views
Consider the following relation R(XYZ) with X as the primary key and Z as the foreign key referencing X with a delete cascade. X Y Z X1 Y1 X7 X3 Y1 X2 X5 Y4 X3 X2 Y2 X1 X9 Y5 X3 X7 Y3 X8 X4 Y2 X2 Suppose tuple (X2, Y2, X1) is deleted, as a result what will be the number of tuples in R after deletion?
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1 answer 10 views
A relation R (ABCDE) with functional dependency F= {AB ->CD, A->E, C->D} The decomposition of R into R1(ABC), R2(BCD) and R3(CDE) (i) lossless join (ii) lossy decomposition (iii) dependency preserving (iv) not dependency preserving (A) i & ii (B) i & iv (C) ii & iii (D) ii & iv
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1 answer 15 views
Consider the following (incomplete) schedule S: T1:R(X), T1:R(Y), T1:W(X), T2:R(Y), T3:W(Y), T1:W(X), T2:R(Y) If all three transactions eventually commit, show the serializability graph.
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0 answers 5 views
For the following information systems determine the entities of interest, their attributes and the relationships that exist between the entities. Draw the E-R diagram for the system. Peoples Information Systems for a village/ward(that stores information about peoples)
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0 answers 8 views
Consider the following (incomplete) schedule S: T1:R(X), T1:R(Y), T1:W(X), T2:R(Y), T3:W(Y), T1:W(X), T2:R(Y) If all three transactions eventually commit, show the serializability graph.
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0 answers 7 views
here is the question. I think the minimum number of the table needed is 4 whereas 5 is given as the answer. please clear my doubt.
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1 answer 16 views
It is 2NF or not ? Just explain this portion.
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0 answers 8 views
Lets suppose, we define a schema with no primary key but there is an attribute(s) with unique and not null constraints. Now default indexing i.e primary indexing is not possible here because of no primary key. Now, at the time of Database design, If i write ... is it necessary to input records in sorted order? or is there any other way possible to apply clustering index over a given database file?
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0 answers 8 views
Given the relational schemas: ENROLL(SID,C_No,Section) - SID and C_No represent student id number, course number respectively TEACH(TID,C_No,Section) - TID represents teacher id number ADVISE(TID,SID) TID is the mentor of SID PRE_REQ(C_No,PRE_C_No) - PRE_C_No is ... List the courses that student Anindya can enroll in, i.e., has passed the necessary prerequisite courses but not the course itself.
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0 answers 6 views
Consider the following relations concerning a driving school. The primary key of each relation is in boldface. STUDENT(S_Name,Class_No,Th_Mark,Dr_Mark) S_Name - student name, Th-Mark - Theory mark, Dr_Mark - driving mark STUDENT_DRIVING_TEACHER(S_Name,Dr_T_Name) Dr_T_Name - driving ... more marks than average theory mark of class 8. f)Find the list of teachers who can drive all the vehicles.
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0 answers 5 views
Is the JOIN operations(natural , left , right) in relational algebra and SQL same or is there any difference based on the condition? Please provide reference.
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0 answers 6 views
How to find the number of relations required for a self-referential relationship with all the cardinalities mapped with total and partial participation? Please provide links to the same.
1 vote
1 answer 49 views
Suppose, R(ABCDE) is a relation, and {AB,CD} are the candidate keys, then: the functional dependency, AC->E a partial dependency? Edit: Actually i wanted to ask if AC->E is in 2NF?
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0 answers 7 views
what is the degree of recursive relationship in ER diagram.
1 vote
2 answers 58 views
Suppose we have two entity sets person, Email and use a relationship Owns. A person own atmost one email account but an email account can be owned by multiple persons. Which of the following is an ER diagram based on above description.
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0 answers 10 views
Find the minimum number of tables in the above ER diagram.
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0 answers 11 views
R(A,B,C,D) is a relation. FD given is:{ AB->C , C->AD } is it in 2NF? is it in 3NF?
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0 answers 7 views
A relation R(A,B,C) has FD A $\rightarrow$ B and other relation M(A, B) has FD A $\rightarrow$ B. Does relation R and M have equivalent FD ?
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0 answers 15 views
So recently I have been studying minimization of ER diagrams and have come across a big confusion. So if 2 entities, E1 and E2 are related to each other with one to one cardinality and E1 has Total participation and E2 has Partial participation, How many minimum tables will ... the answer is 1, but some sources also say that answer should be 2. Also for GATE exam which one should be considered ?
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1 answer 28 views
Consider the following set of Functional dependencies for relational schema R{A,B,C} F={A->BC, B->C, A->B, AB->C} (i) Find the key of relation R
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0 answers 20 views
Why in this question use B-->A ,A-->C ?
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0 answers 6 views
What is right replication policy in database? And how is it different from right biasing?
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1 answer 28 views
is it true that “every strict schedule is cascadeless schedule”?
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0 answers 21 views
Check for recoverable ,cascadeless & strict.
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0 answers 9 views
In Database normalization, I had a question. In the 3rd Normal form, we remove the transitive dependency, so due to this removal, we remove some of the redundant entries. My question is why we need BCNF. How re are removing more redundant entries by using BCNF. please explain this by using an example and compare with 3rd normal form.
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0 answers 35 views
Relation R (A,B,C,D) with FD'S { A->B, B->C, C->D, D->A } then relation R is decomposed into two relations R1 and R2 such that it is satisfying second normal form, third normal form and BCNF and decomposition is lossy. Then how the attributes are distributed in these two decomposed relations R1 and R2? Note: U is the set of all attributes. 1. 2. 3. 4.
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1 answer 24 views
What is degree of Self Referential Relationship? Unary or Binary?
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0 answers 13 views
Given 3 T1, T2 and T3 transactions which have (2,2), (3,2), (4,2) read and write operations respectively the no of schedules possible using these three transactions are A. 1260 B. 630630 C. 6 D. 63000
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3 answers 59 views
Q. R(A,B,C,D,E,F) with {A,BC,CD} candidate keys.How many super keys possible?
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0 answers 82 views
Given the following relations and SQL query: Student (sid, name, age, address, date of birth, level) Book(bid, title, author) Checkout(sid, bid, date_borrowed, date_returned) SELECT S.sid, S.level, C.date_borrowed, C.date_returned FROM Student S, Book B, Checkout C ... correctness of the query using a Relation Connection Graph.[5 marks] d) Represent the query above using a query tree. [5 marks]
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0 answers 32 views
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0 answers 20 views
Hello sir/mam, Today I've been told by our sir that we can write into ROM. Is that specified for mobile ROM or Computer ones or none of them please do clarify my doubt!
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0 answers 14 views
Can Somebody know how to design ER Diagram from this ?
4 votes
4 answers 956 views
Consider the following statements $S1$ and $S2$ about the relational data model: $S1$: A relation scheme can have at most one foreign key. $S2$: A foreign key in a relation scheme $R$ cannot be used to refer to tuples of $R.$ Which one of the following choices is correct? Both $S1$ and $S2$ are true $S1$ is true and $S2$ is false $S1$ is false and $S2$ is true Both $S1$ and $S2$ are false
1 vote
2 answers 556 views
The relation scheme given below is used to store information about the employees of a company, where $\textsf{empId}$ is the key and $\textsf{deptId}$ indicates the department to which the employee is assigned. Each employee is assigned to exactly ... than the average salary of employees in the department employees in the company female employees in the department female employees in the company
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2 answers 704 views
Let $S$ be the following schedule of operations of three transactions $T_1$, $T_2$ and $T_3$ in a relational database system: $R_2(Y), R_1(X), R_3(Z), R_1(Y)W_1(X), R_2(Z), W_2(Y), R_3(X), W_3(Z)$ Consider the statements $P$ and $Q$ below: $P$: $S$ is conflict- ... correct? Both $P$ and $Q$ are true $P$ is true and $Q$ is false $P$ is false and $Q$ is true Both $P$ and $Q$ are false
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1 answer 611 views
Suppose the following functional dependencies hold on a relation $U$ with attributes $P,Q,R,S$, and $T$: $P \rightarrow QR$ $RS \rightarrow T$ Which of the following functional dependencies can be inferred from the above functional dependencies? $PS \rightarrow T$ $R \rightarrow T$ $P \rightarrow R$ $PS \rightarrow Q$
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