# Recent questions and answers in Databases

1
A primary key for an entity is a candidate key any attribute a unique attribute a superkey
2
Choose the correct alternatives (More than one may be correct). Indicate which of the following statements are true: A relational database which is in 3NF may still have undesirable data redundancy because there may exist: Transitive functional ... trivial functional dependencies involving prime attributes only on the left-side. Non-trivial functional dependencies involving only prime attributes.
3
Consider three data items $D1, D2,$ and $D3,$ and the following execution schedule of transactions $T1, T2,$ and $T3.$ In the diagram, $R(D)$ and $W(D)$ denote the actions reading and writing the data item $D$ ... $T2; T3; T1$ The schedule is serializable as $T2; T1; T3$ The schedule is serializable as $T3; T2; T1$ The schedule is not serializable
4
The E-R model is expressed in term of I. Entities II. The relationship among entities. III. The attributes of the entities. IV. Functional relationship. (A) I, II (B) I, II, IV (C) II, II, IV (D) I, II, III
5
In a relational Schema, each tuple is divided into fields called relations domains queries none of these
6
The $\text{E-R}$ model is expressed in terms of : Entities The relationship among entities The attributes of the entities Then (i) and (iii) (i) and (ii) (ii) and (iii) None of the above
7
An entity has: (i) a set of properties (ii) a set of properties and values for all the properties (iii) a set of properties and the values for some set of properties may non-uniquely identify an entity (iv) a set of properties and the values for some set of properties may uniquely identify an entity Which of the above are valid? (i) only (ii) only (iii) only (iv) only
8
An Entity-relationship diagram is a tool to represent Data model Process model Event model Customer model
9
Suppose we have a database consisting of the following three relations. $\text{FREQUENTS (student, parlor)}$ giving the parlors each student visits. $\text{SERVES (parlor, ice-cream)}$ ... parlor) Express the following in SQL: Print the students that frequent at least one parlor that serves some ice-cream that they like.
10
Suppose a database consist of the following relations: SUPPLIER (SCODE,SNAME,CITY). PART (PCODE,PNAME,PDESC,CITY). PROJECTS (PRCODE,PRNAME,PRCITY). SPPR (SCODE,PCODE,PRCODE,QTY). Write SQL programs corresponding to the following queries: Print PCODE values for parts supplied to ... specified part to a project in the second city, but do not print the triples in which the two CITY values are same.
11
An entity instance is a single occurrence of an ______. Entity type Relationship type Entity and relationship type None of these
12
Consider the following relational schema: $\text{Suppliers}(\underline{\text{sid:integer}},\text{ sname:string, city:string, street:string})$ $\text{Parts}(\underline{\text{pid:integer}}, \text{ pname:string, color:string})$ ... the names of all suppliers who have supplied only non-blue part. Find the names of all suppliers who have not supplied only blue parts.
13
What is the maximum number of records that can be indexed in B+ tree of level $4$ ,order $10$ where root is at level $1$ ? As the order of tree is $10$, nodes in the last level of b+ tree should contain $10$ record pointers (number of record pointers = order of ... $10-1 = 9$ record pointers. Which one is correct?
14
Consider the relation $R(P,Q,S,T,X,Y,Z,W)$ with the following functional dependencies. $PQ\rightarrow X;\quad P\rightarrow YX;\quad Q\rightarrow Y; \quad Y\rightarrow ZW$ Consider the decomposition of the relation $R$ into the constituent relations according to ... , but $D_2$ is a lossless decomposition Both $D_1$ and $D_2$ are lossless decompositions Both $D_1$ and $D_2$ are lossy decompositions
15
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
16
If every non-key attribute is functionally dependent on the primary key then the relation will be in   A. 1NF                          B. 2NF                        C. 3NF                             D. 4NF I think the answer should be 2NF, but in the key it is given 3NF
17
Consider the schema $R=(S,T, U, V)$ and the dependencies $S \rightarrow T, T \rightarrow U, U \rightarrow V$ and $V \rightarrow S$. Let $R = (R1\text{ and } R2)$ be a decomposition such that $R1 \cap R2 \neq \phi$. The decomposition is not in $2NF$ in $2NF$ but not $3NF$ in $3NF$ but not in $2NF$ in both $2NF$ and $3NF$
18
Minimum no of table for this ER diagram
19
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
20
Suppose a database system crashes again while recovering from a previous crash. Assume checkpointing is not done by the database either during the transactions or during recovery. Which of the following statements is/are correct? The same undo and redo list ... any further All the transactions that are already undone and redone will not be recovered again The database will become inconsistent
21
Let $r_i(z)$ and $w_i(z)$ denote read and write operations respectively on a data item $z$ by a transaction $T_i$. Consider the following two schedules. $S_1: r_1(x)r_1(y)r_2(x)r_2(y)w_2(y)w_1(x)$ ... $S_2$ is conflict serializable Both $S_1$ and $S_2$ are conflict serializable Niether $S_1$ nor $S_2$ is conflict serializable
1 vote
22
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
1 vote
23
A relation $r(A, B)$ in a relational database has $1200$ tuples. The attribute $A$ has integer values ranging from $6$ to $20$, and the attribute $B$ has integer values ranging from $1$ to $20$. Assume that the attributes $A$ and $B$ are independently distributed. The estimated number of tuples in the output of $\sigma _{(A>10)\vee(B=18)}(r)$ is ____________.
24
The following relation records the age of $500$ employees of a company, where $empNo$ ( indicating the employee number) is the key: $empAge(\underline{empNo},age)$ ... one other employee Employee numbers of all employees whose age is not the minimum Employee numbers of all employees whose age is the minimum
25
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? $PS \rightarrow T$ $R \rightarrow T$ $P \rightarrow R$ $PS \rightarrow Q$
1 vote
26
A primary key, if combined with a foreign key creates parent child relationship between the tables that connect them many-to-many relationship between the tables that connect them network model between the tables that connect them none of these
27
A relation (from the relational database model) consist of a set of tuples, which implies that a) relational model supports multi-valued attributes whose values can be represented in sets. b) for any two tuples, the value associated with all of their ... value associated with one or more of their attributes must differ. d) all tuples in a particular relation may have different attributes.
28
Let $M$ and $N$ be two entities in an $E-R$ diagram with simple single value attributes. $R_{1}$ and $R_{2}$ are two relationship between $M$ and $N$, where as $R_{1}$, is one-to-many and $R_{2}$, is many-to-many. The minimum number of tables required to represent $M, N, R_{1}$, and $R_{2}$, in the relational model are ___________. $4$ $6$ $7$ $3$
29
Given relations $R(w,x)$ and $S(y,z),$ the result of SELECT DISTINCT $w,x$ from $R,S$ $R$ has no duplicates and $S$ is non-empty $R$ and $S$ have no duplicates $S$ has no duplicates and $R$ is non-empty $R$ and $S$ has the same number of tuples
30
When transaction $Ti$ requests a data item currently held by $Tj,Ti$ is allowed to wait only if it has a timestamp smaller than that of $Tj$ (that is $Ti$ is order than Tj). Otherwise, $Ti$ is rolled back (dies). This is Wait-die Wait-wound Wound-wait Wait
31
Which of the following desired features are beyond the capability of relational algebra? Aggregate Computation Multiplication Finding transitive closure All of the above
32
Which one is correct w.r.t. RDBMS? primary key $\subseteq$ super key $\subseteq$ candidate key primary key $\subseteq$ candidate key $\subseteq$ super key super key $\subseteq$ candidate key $\subseteq$ primary key super key $\subseteq$ primary key $\subseteq$ candidate key
33
Consider the relational schema $\text{R(A B C D)}$ with following functional dependency set $F=\{A\rightarrow BC,C\rightarrow D\};$ The relation $\text{R}$ is in $2$NF BCNF $3$NF $1$NF
34
Consider a relational schema $S=(U,V,W,X,Y,Z)$ on which the following functional dependencies hold: $(U \rightarrow V, VW \rightarrow X, Y \rightarrow W, X \rightarrow U)$ Which are the candidate keys among following options? $UY, VY$ $UY, VY, XY$ $UYZ, VYZ, VWZ$ $UYZ, VYZ, XYZ$
35
In the context of concurrency control, a given pair of operations in a schedule is called conflict schedule if At least one of the operations is write operation Both the operations are performed on the same data item Both the operations are performed by different transactions Both the operations are performed on different ... $(b)$ and $(c)$ only $(a)$, $(c)$ and $(d)$ only $(c)$ and $(d)$ only
1 vote
36
Match $\text{List I}$ with $\text{List II}$ Choose the correct answer from the options given below: $A-II, B-IV, C-III, D-I$ $A-IV, B-I, C-II, D-III$ $A-II, B-I, C-IV, D-III$ $A-III, B-IV, C-I, D-II$
37
Consider the following table structures related to a university for the below question. EMPLOYEE NAME VARCHAR (30) NOT NULL, EID VARCHAR (10) NOT NULL, DEPTNO INT (5) NOT NULL, HODEID VARCHAR (10), SALARY INT (10), PRIMARY KEY (EID), FOREIGN KEY (HODEID) ... 20,30,40); SELECT DISTINCT EMPID FROM PROJECTWORK WHERE PROJNO IN(20,30,40); SELECT DISTINCT EMPID FROM PROJECTWORK WHERE PROJNO=20,30,40;
Consider the following table structures related to a university for the below question. EMPLOYEE NAME VARCHAR (30) NOT NULL, EID VARCHAR (10) NOT NULL, DEPTNO INT (5) NOT NULL, HODEID VARCHAR (10), SALARY INT (10), PRIMARY KEY (EID), FOREIGN KEY (HODEID) REFERENCES ... $II$ are false Statement $I$ is correct but Statement $II$ is false Statement $I$ is incorrect but Statement $II$ is true
Consider the following table structures related to a university for the below question. EMPLOYEE NAME VARCHAR (30) NOT NULL, EID VARCHAR (10) NOT NULL, DEPTNO INT (5) NOT NULL, HODEID VARCHAR (10), SALARY INT (10), PRIMARY KEY (EID), FOREIGN KEY (HODEID) REFERENCES EMPLOYEE (EID), ... EID Choose the correct answer from the options given below: $a$ and $b$ only $a$ and $c$ only $b$ only $c$ only
Consider the following table structures related to a university for the below question. EMPLOYEE NAME VARCHAR (30) NOT NULL, EID VARCHAR (10) NOT NULL, DEPTNO INT (5) NOT NULL, HODEID VARCHAR (10), SALARY INT (10), PRIMARY KEY (EID), FOREIGN KEY (HODEID) REFERENCES EMPLOYEE (EID), FOREIGN ... correct answer from the options given below: $a$ and $b$ only $a$ and $c$ only $b$ and $c$ only $a$ only