# Recent questions tagged databases

1
For a $B^+$ - tree of order $d$ with $n$ leaf nodes, the number of nodes accessed during a search is $O(\_)$.
2
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
3
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
4
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
5
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? $PS \rightarrow T$ $R \rightarrow T$ $P \rightarrow R$ $PS \rightarrow Q$
6
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
7
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 ____________.
8
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
9
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
10
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
11
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? $UY, VY$ $UY, VY, XY$ $UYZ, VYZ, VWZ$ $UYZ, VYZ, XYZ$
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
Match $\text{List I}$ with $\text{List II}$ Choose the correct answer from the options given below: $A-II, B-IV, C-III, D-I$ $A-IV, B-I, C-II, D-III$ $A-II, B-I, C-IV, D-III$ $A-III, B-IV, C-I, D-II$