GATE CS Databases questions

Consider the following relational schema: employee (empId,empName,empDept) customer (custId,custName,salesRepId,rating) salesRepId is a foreign key referring to empId of the employee relation. Assume that each employee makes a sale to at least one customer. What does the following query return? SELECT empName FROM employee E WHERE NOT EXISTS (SELECT custId …

Consider the relational schema given below, where eId of the relation dependent is a foreign key referring to empId of the relation employee. Assume that every employee has at least one associated dependent in the dependent relation. employee (empId, empName, empAge) dependent (depId, eId, depName, depAge) Consider the following relational algebra query: …

Consider the transactions $T1, T2, \:\text{and} \:T3$ and the schedules $S1 \:\text{and} \:S2$ given below. $T1: r1(X); r1(Z); w1(X); w1(Z)$ $T2: r2(Y); r2(Z); w2(Z)$ $T3: r3(Y); r3(X); w3(Y)$ $S1: r1(X); r3(Y); r3(X); r2(Y); r2(Z); w3(Y); w2(Z); r1(Z); w1(X); w1(Z)$ $S2: r1(X); r3(Y); r2(Y); r3(X); r1(Z); r2(Z); w3(Y); w1(X); w2(Z); w1(Z)$ …

A prime attribute of a relation scheme $R$ is an attribute that appears

What is the optimized version of the relation algebra expression $\pi_{A1}(\pi_{A2}(\sigma_{F1}(\sigma_{F2}(r))))$, where $A1, A2$ are sets of attributes in $r$ with $A1 \subset A2$ and $F1,F2$ are Boolean expressions based on the attributes in $r$?

Relation $R$ has eight attributes $\text{ABCDEFGH}$. Fields of $R$ contain only atomic values. $F$= $\text{{CH→G, A→BC, B→CFH, E→A, F→EG}}$ is a set of functional dependencies $(FDs)$ so that $F^+$ is exactly the set of $FDs$ that hold for $R$. How many candidate keys does the relation $R$ have?

Consider the following relational schema. Students(rollno: integer, sname: string) Courses(courseno: integer, cname: string) Registration(rollno: integer, courseno: integer, percent: real) Which of the following queries are equivalent to this query in English? “Find the distinct names of all students who score more than $90\%$ in the course numbered 107” …

An index is clustered, if

Consider the following relations $A, B$ and $C:$ …

Consider the following relations $A, B$ and $C:$ …

Suppose $R_{1} (\underline{A}, B)$ and $R_{2} (\underline{C}, D)$ are two relation schemas. Let $r_{1}$ and $r_{2}$ be the corresponding relation instances. $B$ is a foreign key that refers to $C$ in $R_{2}$. If data in $r_{1}$ and $r_{2}$ satisfy referential integrity constraints, which of the following is ALWAYS TRUE?

Consider the following transactions with data items $P$ and $Q$ initialized to zero: …

Which of the following statements are TRUE about an SQL query? P : An SQL query can contain a HAVING clause even if it does not have a GROUP BY clause Q : An SQL query can contain a HAVING clause only if it has a GROUP BY clause R : All attributes used in the GROUP BY clause must appear in the SELECT clause S : Not all attributes used in the GROUP BY clause …

Given the basic ER and relational models, which of the following is INCORRECT?

Which of the following is TRUE?

Database table by name $\text{Loan\_Records}$ is given below. …

Consider a relational table $r$ with sufficient number of records, having attributes $A_1, A_2, \dots ,A_n$ and let $1 \leq p \leq n$. Two queries $Q1$ and $Q2$ are given below. $Q1: \pi_{A_1, \dots ,A_p} \left(\sigma_{A_p=c}\left(r\right)\right)$ where $c$ is a constant …

Consider a database table T containing two columns $\text{X}$ and $\text{Y}$ each of type $\text{integer}$. After the creation of the table, one record $\text{(X=1, Y=1)}$ is inserted in the table. Let $\text{MX}$ and $\text{MY}$ denote the respective maximum values of $\text{X}$ and $\text{Y}$ among all records in the table at any point in …

Consider a relational table with a single record for each registered student with the following attributes: $\text{Registration\_Num:}$ Unique registration number for each registered student $\text{UID:}$ Unique identity number, unique at the national level for each citizen $\text{BankAccount\_Num:}$ Unique account number at the bank. A student can …

The following functional dependencies hold for relations $R(A, B, C)$ and $S(B, D, E).$ $B \to A$ $A \to C$ The relation $R$ contains $200$ tuples and the relation $S$ contains $100$ tuples. What is the maximum number of tuples possible in the natural join $R \bowtie S$?