Recent questions and answers in Databases

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Gateoverflow question on B+ tree - Self Doubt
https://gateoverflow.in/258022/dbms-basic-test1 Int the above question, as per the diagram, the leaves are supposed to be in level 4 and so the number of children in level 3 which equals to 27 as per calculation means the number of child pointers to level 4 that is the leaf node level is actually 27. Am I correct ?

asked 7 hours ago in Databases by user2525 (1.6k points) | 6 views

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B tree and B+ tree - Made Easy / Gateoverflow
For the below question, https://gateoverflow.in/285557/madeeasy-test-series-databases-b-tree Can anyone explain option B and option D ? I mean what they actually mean to say ?

asked 8 hours ago in Databases by user2525 (1.6k points) | 4 views

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

asked 15 hours ago in Databases by Abhinav999 (106 points) | 5 views

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iGate Bhillai Test: DBMS

asked 15 hours ago in Databases by Abhinav999 (106 points) | 3 views

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iGate Bhilai Test 2020:dbms

asked 15 hours ago in Databases by Abhinav999 (106 points) | 4 views

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Foreign key - Self Doubt
When it comes to inserting something in a foreign key table, we cant put null values. But when it comes to deleting something from referenced table, we can perform ON DELETE SET NULL operation and make the foreign key value in a particular tuple as NULL. So, a foreign key can’t remain null while inserting but it can be null while deletion. Is my approach correct ?

answered 1 day ago in Databases by Rudr Pawan (419 points) | 39 views

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View Serializability
Can someone write the entire steps and rules of polygraph test to check view serializability. P.S. : Kindly, dont give me links. Please write the rules in a stepwise manner if known.

asked 2 days ago in Databases by user2525 (1.6k points) | 5 views

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ACE Test Series - Normalization
Regarding statement Q, I don’t think it will violate 3NF because whatever be the R.H.S. if L.H.S. is superkey, then it is in BCNF and ultimately in 3NF. Therefore, it is allowed in 3NF and so the statement is supposed to be right. Is my approach correct ?

asked 2 days ago in Databases by user2525 (1.6k points) | 12 views

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Lossless Decomposition - Self Doubt
https://gateoverflow.in/208190/lossy-or-lossless In the above question : FDs are AB→C,AC→B,AD→E,B→D,BC→A,E→G. R1 ( ABC ) : AB → C AC → B BC → A R2 ( ACDE ) : AD → E R3 ( ADG ) has empty FDs. So, the above decomposition is not ... a key order to check lossless decomposition ? Do we have 2 consider the closure of original fds to prove AD as key for R3 ( ADG ) ?

asked 3 days ago in Databases by user2525 (1.6k points) | 9 views

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Self Doubt - 3NF Decomposition
I know that BCNF may not satisfy dependency preserving but it should be lossless. So, when we are decomposing a relation for satisfying BCNF, we don’t care about the dependency preservation condition. But what about 3NF ? Is it compulsory to check for dependency preservation condition after a table has been decomposed to satisfy 3NF ?

asked 3 days ago in Databases by user2525 (1.6k points) | 14 views

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E R diagram default participation
If participation is not given then default is partial or total???

asked 4 days ago in Databases by Choudhary Iitd (102 points) | 5 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 4 days ago in Databases by user2525 (1.6k points) | 11 views

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Relational Algebra - CSE Doubt
I know projection operator in relational algebra eliminates duplicates. But suppose a table contains 2 duplicate rows. Sql retains the duplicates. But what about selection operator in relational algebra. Does it eliminates duplicates ? Moreover ... operator in relational algebra eliminates duplicates or is there any exception too for operators in relational algebra ?

answered 6 days ago in Databases by Dhananjay15 (104 points) | 16 views

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Tuple Relational Calculus - Doubt
I know abt universal quantifier ∀ and existential quantifier ∃ . But in tuple relational calculus, how we will interpret by looking at the question when to use ∀ and when to use ∃ ? For example : in the below question, Find the names and ages of ... in the above question, we are using ∃ instead of ∀. My doubt is when shall we apply ∀ and ∃ inTRC questions ?

answered Aug 16 in Databases by Hirak (1.3k points) | 18 views

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#MadeEasywork
Number of Conflict Equal and View Equal Schedules How many Conflict Serializable and View serializable schedules for the Schedule given below S:r1(A),w1(B),w1(C),r2(A),w2(B),w2(C)

asked Aug 12 in Databases by ssanjivv (104 points) | 1 view

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Gate previous year ques.
In a file which contains 1 million records and the order of the tree is 100, then what is the maximum number of nodes to be accessed if B+ tree index is used? I need proper explanation I did not understood the answer of this question as it was already posted.

asked Aug 11 in Databases by Aditya Anand (102 points) | 5 views

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1 answer

Decompose to BCNF.

answered Aug 8 in Databases by user2525 (1.6k points) | 6 views

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3 answers

GATE DBMS Question on Normalization
Kindly show your solution. I am not able to decompose the relation. Thank you.

answered Aug 7 in Databases by ilejudege | 31 views

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1 answer

Superkey question
Consider the following relation: R (A1, A2, ….An) and every (n-2) attributes of R forms a candidate key. How many super keys are there in R?

answered Aug 5 in Databases by sagar2405 (192 points) | 18 views

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SQL question DBMS
Kindly show the output also. Thank you.

answered Aug 4 in Databases by Satbir (1k points) | 14 views

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DBMS Left Outer Join Question
The answer is given 6. I am getting 6 too but I want to confirm the output. SID GATEID 12 101 12 104 15 101 16 103 25 102 27 NULL Am I correct?

asked Aug 4 in Databases by DukeThunders (208 points) | 7 views

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Precedence graph question
Consider 2 schedules S1 and S2 with same set of transactions and precedence graph of S1 is same as precedence graph of S2. Which of the following statement is True? (a) Both S1 and S2 are conflict equal and conflict serializable schedule ... explain what the question means. This was asked before but there was no explanation. https://gateoverflow.in/196697/precedence-graph

asked Aug 4 in Databases by DukeThunders (208 points) | 5 views

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DBMS 2PL and Time Stamp Ordering question 2
2PL generates serializability, but it does not prevent deadlocks. 2PL has 2 phases: growing and shrinking. Which of the following rules are used to govern the 2PL protocol? (a) 2 transactions cannot have conflicting locks (b) No unlock operation can ... does it want to say? For option A, 2PL has deadlocks, so doesn't it mean it has conflicting locks?

asked Aug 4 in Databases by DukeThunders (208 points) | 3 views

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DBMS 2PL and Time Stamp Ordering question
Choose the False statement: (a) time stamp protocol is deadlock free (b) 2- phase locking generates serializability (c) strict 2-phase locking is deadlock free (d) time stamp protocol may not result recoverable schedule

asked Aug 4 in Databases by DukeThunders (208 points) | 9 views

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1 answer

DBMS Question on Normalization 2

answered Aug 3 in Databases by user2525 (1.6k points) | 21 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 (208 points) | 4 views

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VIRTUAL GATE SQL
Query1: SELECT eno FROM emp WHERE deptno=10 union SELECT eno FROM emp WHERE deptno=20 Query2: SELECT eno FROM emp WHERE deptno=10 or deptno=20 Let the result of Queryl is Q1 and the result of Query2 is Q2, then which of the following is always true? (A) Q1=Q2 (B) Q1 $\subseteq$ Q2 (C) Q2 $\subseteq$ Q1 (D) Data is insufficient

asked Jul 30 in Databases by aditi19 (134 points) | 6 views

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Virtual GATE MVD Question
Consider the following table the answer is there are two MVD in this relation Department ->>Part Department ->>Job how does the second MVD hold? d3 doesn’t have multiple values for job.

asked Jul 30 in Databases by aditi19 (134 points) | 3 views

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Gate CS 2008
Consider a file of 16384 records. Each record is 32 bytes long and its key field is of size 6 bytes. The file is ordered on a non-key field, and the file organization is unspanned. The file is stored in a file system with block size 1024 bytes, and the ... 4 512 and 5 While calculating the blocks for file why we haven't multiplied with 32 bytes since the records are given of 32 bytes ?

asked Jul 30 in Databases by Alakhator (355 points) | 8 views

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DBMS File organization
In secondary indexing we have number of index enteries equal to number of records. But what if the non-key on which it is based has repititions? Will there be number of enteries equal to numbe rof records in this case?

answered Jul 29 in Databases by Satbir (1k points) | 2 views

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doubt on secondary Index
This image is from NAVATHE book. for seconadry Index(in case of CK field) we can use sparse indexing as we do for PK, because every CK value is unique & it can uniquely identify each tuple. then what stops us from doing sparse indexing incase of CK field??? why NON-key row is Dense or Nondense in the image ??? for non-key we should always use dense indexing, isn’t it???

asked Jul 29 in Databases by MRINMOY_HALDER (110 points) | 3 views

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1 answer

Nptel - Fundamentals of Database Systems Assignment

answered Jul 28 in Databases by Hirak (1.3k points) | 11 views

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2 answers

new gradiance
Consider the following schedule S of two transactions: r1(X), r2(Y), w1(Y), c1, w2(Z), c2. Tell whether S is serial? serializable? recoverable? ACR (avoids cascading rollback)? strict? Then, indicate which of the following is TRUE about S? a) S ... and S is strict as per me there is no dirty read hence cascading rollbacks should be avoided . the schedule doesn't look strict either

answered Jul 25 in Databases by APOORV PANSE (190 points) | 4 views

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1 answer

ER-Model Self Doubt
What is the degree of the recursive relationship?

answered Jul 25 in Databases by APOORV PANSE (190 points) | 9 views

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1 answer

#B+tree, #Madeeasy

answered Jul 23 in Databases by APOORV PANSE (190 points) | 7 views

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Gradeup quiz
Which cardinality best describes relationship runs where all team has drag experiment to runs?

asked Jul 22 in Databases by aditi19 (134 points) | 5 views

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#Navathe #Indexing
“A file can have at most one physical ordering field,so it can have at most one primary index or one clustering index,but not both”. There could exist 2-such fields in a file such that ordering the file on the basis of one-field automatically orders it PHYSICALLY w.r.t another field too. I am not getting why a file can have ATMOST one physical ordering field.

asked Jul 22 in Databases by Kaurbaljit (102 points) | 3 views

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1 answer

Database book
pls explain with examples

answered Jul 16 in Databases by user2525 (1.6k points) | 12 views

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1 answer

#Graph Based protocols
In a graph based protocol,after locking on any data item initially,can a transaction request for a lock on a data item present as the Root of the tree?

answered Jul 13 in Databases by Hirak (1.3k points) | 6 views

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Serializability of schedules
What is the difference between dependency graph(used to test conflict serializability) and poly grraph(for view serializability)? Give an example if possible.

asked Jul 11 in Databases by Shriya Reddy (104 points) | 4 views