The number of attributes in a relation is called the ______ of the relation.
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Correct answer: (A) Degree
Explanation
The degree of a relation is its number of attributes (columns). Cardinality is the number of tuples (rows).
DSSSB TGT / PGT · Computer Science
DBMS & SQL Previous Year Questions (page 2)
227 DBMS & SQL (Computer Science) questions asked in DSSSB TGT / PGT previous year papers, each with the correct answer and explanation. Read them free on UTpaper, or attempt the full papers as timed online tests.
- 227 questions
- Official answer key
- Free
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Digital Logic & Number Systems 194Computer Networks 177Operating Systems 161Data Structures 151Programming in C/C++ 89Web Technologies 68Algorithms 66Computer Organization & Architecture 66Discrete Mathematics 66OOP 63Java 46E-Commerce & IT Management 41Computer Fundamentals & MS Office 34Python 29Computer Graphics & Multimedia 28Software Engineering 23Cyber Security 13AI, ML & Data Science 11
A child has a schema for a dog based on his experience with his pet, then when he sees another dog in the garden, he is able to recognize the animal. Which process of cognitive development is highlighted in the statement?
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Correct answer: (A) Assimilation
Explanation
Fitting a new experience (another dog) into an existing schema is assimilation in Piaget's theory. Accommodation means changing the schema itself.
With SQL, how can you return the number of records in the "Persons" table?
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Correct answer: (A) SELECT COUNT (*) FROM Persons
Explanation
Options (b) and (c) are printed identically in the source book.
What will the following code result in?
import pandas as pd
pd.Series ([10,20], index = ['A', 'B', 'C'])
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Correct answer: (A) ValueError
Explanation
The data list has 2 values but the index has 3 labels. pandas cannot match the lengths, so it raises a ValueError ("Length of values does not match length of index").
Which of the following attribute of the <TABLE> tag specifies the amount of space between the border and the contents of the cell?
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Correct answer: (C) CELL PADDING
Explanation
CELLPADDING sets the space between a cell's border and its content. CELLSPACING sets the space between neighbouring cells.
What is the correct usage of the FRAMEBORDER attribute of the <FRAME> tag in HTML ?
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Correct answer: (D) Specifies whether the border should be visible or not
Explanation
FRAMEBORDER takes 1 or 0 (yes or no) and controls whether a border is shown around the frame. It does not set the border colour or the scrollbars.
Which of the following is not an example of an application of a Database ?
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Correct answer: (A) VIDEO Editing
Explanation
Video editing works on audio and video media streams and is not organised around stored records. Profile, result and inventory systems are classic database applications.
Which of the following options appropriately represent the relationship shown in the diagram ?
Diagram: entity box E1 is joined to entity box E2 by a line labelled R; the line ends in a crow's-foot (many) symbol at the E1 side and has a plain end at the E2 side.
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Correct answer: (C) MANY - TO - ONE
Explanation
The crow's foot (many) is on the E1 side and the plain (one) end is on the E2 side. Many E1 entities relate to one E2 entity, so the relationship is many-to-one.
Which of the following cannot be represented as a tree ?
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Correct answer: (C) Customer calls in a call centre
Explanation
Customer calls in a call centre are served in arrival order (first in, first out), so they form a queue, not a hierarchy. Directories, a table of contents and arithmetic expressions are naturally hierarchical trees.
______ is a sequence of memory read-write operations that are atomic.
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Correct answer: (D) Memory transaction
Explanation
In transactional memory, a memory transaction is a sequence of memory read-write operations that is atomic: either all of them take effect (commit) or none do.
In relational databases, the natural join of two tables is :
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Correct answer: (D) Combination of Projection and filtered Cartesian Product.
Explanation
A natural join takes the Cartesian product, keeps the rows where common attributes are equal (selection), then projects away the duplicate columns. So it is a projection of a filtered Cartesian product.
Consider the database table "Persons" having persons_ID as the primary key:
person_ID | Name | Age
1000 | Rajan | 40
- | Jatin | -45
1001 | Rajesh | 35
What are the constraints violated by the above table ?
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Correct answer: (C) Entity and domain integrities
Explanation
A missing person_ID breaks entity integrity, because a primary key cannot be null. An age of −45 is outside the valid domain, so domain integrity is also broken.
What is the output of the following C program?
# include
int main ( )
{
int index;
for (index = 1; index < = 5; index ++)
{
printf ("%d", index);
if (index = = 3)
continue;
}
}
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Correct answer: (B) 12345
Explanation
printf runs before the if statement, so continue only skips the (empty) rest of the loop body. Every value from 1 to 5 is printed: 12345.
How many rows are there in a truth table having 'n' variables?
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Correct answer: (D) 2ⁿ
Explanation
Each of the n variables can be 0 or 1, giving 2ⁿ input combinations, so the truth table has 2ⁿ rows.
What is the relation between N select inputs and M inputs lines in a multiplexer?
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Correct answer: (B) 2^N = M
Explanation
N select lines can address 2ᴺ inputs, so a multiplexer with M data inputs needs N select lines where 2ᴺ = M.
Which of the following is NOT an attribute of good programming languages?
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Correct answer: (D) Non portability
Explanation
Portability (running on different machines) is a desirable attribute of a good language, so non-portability is not one. Clarity, abstraction and ease of verification are all good attributes.
What is the relation between object and class in an object oriented programming?
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Correct answer: (C) Object is instance of class
Explanation
A class is a blueprint, and an object is an instance of that class created in memory.
Consider a n × n tri-diagonal sparse matrix A. Suppose we want to store sparse A in a one-dimensional array. What is the index of the (i,j)th element of A in the one-dimensional array?
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Correct answer: (B) 2i + j − 2
Explanation
Row-major with 1-based indexes, rows before row i hold 3(i−1) − 1 elements, and (i, j) is the (j − i + 2)th element of row i. Total = 3i − 4 + j − i + 2 = 2i + j − 2.
Using division method [n(k) = k mod m], at which position 177 and 197 key values are stored in hash table when the size of hash table is 57?
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Correct answer: (A) 6, 26
Explanation
177 mod 57 = 177 − 171 = 6 and 197 mod 57 = 197 − 171 = 26.
In C++, "Out-of-range-index" belong to ________ type exception while keyboard interrupts are called ________ exceptions.
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Correct answer: (B) Synchronous; asynchronous
Explanation
Errors such as out-of-range index come from the program's own execution, so they are synchronous. Events beyond the program's control, such as keyboard interrupts, are asynchronous.
What is join operation in Structure Query Language (SQL)?
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Correct answer: (C) Join is an operation used to combine rows from two or more tables based on one or more common fields between them.
Explanation
A JOIN combines rows from two or more tables based on a related (common) column between them.
Which of the following is NOT a part of Data Definitions Language in Relational Database Management System?
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Correct answer: (B) Insert table
Explanation
INSERT is a DML command (and is used as INSERT INTO, not "insert table"). CREATE, ALTER and DROP TABLE are DDL commands.
Match the following formal relational term with informal equivalents.
i. Relation — A. Row
ii. Tuple — B. Value
iii. Attribute — C. Table
iv. Domain — D. Column
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Correct answer: (B) i-3, ii-1, iii-4, iv-2
Explanation
Note: in the official paper the options refer to A, B, C, D as 1, 2, 3, 4 respectively.
Write the name of the relational algebra operation as per the given order of their notation.
Π, X, σ
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Correct answer: (B) Projection, Cartesian product, select
Explanation
Π is projection (choose columns), × is Cartesian product, and σ is selection (choose rows).
Consider the following relation schema of students.
STUDENT (Rollno, Name, DOB, Marks, Gender)
Which of the given query is equivalent to this query in English? "Find the tuples of student having marks above 80".
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Correct answer: (A) σ Marks>80 (STUDENT)
Explanation
Selecting tuples (rows) that satisfy a condition uses σ: σ Marks>80 (STUDENT). Π selects columns, not rows.
What is Denormalization in Relational Database Management System?
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Correct answer: (A) Denormalization is the process of increasing redundancy to improve performance
Explanation
Denormalization deliberately adds redundancy (merging tables or duplicating data) to cut joins and improve read performance.
Which of the following statement(s) is/are correct regarding Structured Query Language (SQL)?
I. The datatype FLOAT can hold numbers with decimal points.
II. The datatype BIGINT occupies 16 bytes.
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Correct answer: (A) Only I
Explanation
FLOAT stores numbers with decimal points, but BIGINT occupies 8 bytes, not 16. So only I is correct.
Which of the following statement is a part of Data Manipulative Language in Structured Query Language?
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Correct answer: (A) Delete
Explanation
DELETE is a DML command because it manipulates data. ALTER TABLE is DDL, and copy/paste are not SQL statements.
What is the cardinality and degree of relation having 50 Tuples and 20 Attributes?
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Correct answer: (C) Cardinality – 50 Degree – 20
Explanation
Cardinality is the number of tuples (50), and degree is the number of attributes (20).
Which of the following statement(s) is/are correct regarding COUNT functions in Structured Query Language of Relational Database Management System?
I. COUNT(*) is used to count the number of values in a column.
II. COUNT() is used to count the number of rows of the query result.
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Correct answer: (D) Neither I nor II
Explanation
Both statements are reversed: COUNT(*) counts all rows of the result, while COUNT(column) counts the non-NULL values in a column. So neither is correct.
Which of the following is NOT an element of Database?
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Correct answer: (D) Frontend
Explanation
A database includes its schema, data, relationships and constraints. A frontend is the user interface application, not part of the database.
Which of the following statement(s) is/are correct regarding single row functions in structured query language?
I. INSERT() is a numeric function.
II. ROUND() is a numeric function.
III. LENGTH() is a character function.
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Correct answer: (B) Both II and III
Explanation
ROUND() is a numeric function and LENGTH() is a character function. INSERT() (e.g., in MySQL) is a string function, not a numeric one.
What is self join in Database Management System?
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Correct answer: (B) In a self-join, a table is joined to itself
Explanation
A self join joins a table to itself, usually using aliases, e.g., to pair employees with their managers in the same table.
Which one of the following is NOT a part of the ACID properties of database transaction?
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Correct answer: (C) Instance
Explanation
ACID stands for Atomicity, Consistency, Isolation and Durability. "Instance" is not one of them.
In Structured Query Language, what is the GROUP BY clause?
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Correct answer: (B) It groups the rows together that contain the same values in a specific column
Explanation
GROUP BY puts rows with the same values in the given column(s) into groups, usually for aggregates like SUM or COUNT.
Which of the following statement(s) is/are correct regarding Data Dictionary in Database Management System?
I. Data Dictionary is a collection of definitions, rules and advisories of data designed to be used as a reference with the data warehouse.
II. Data Dictionary is the area of memory allocated for data storage.
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Correct answer: (A) Only I
Explanation
A data dictionary is a metadata repository that holds definitions, rules and descriptions of the data. It is not a memory area for storing data.
Which of the following is not an example of Simulation and Modeling?
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Correct answer: (B) Computer table
Explanation
Video games, flight simulators and logic-gate simulations all model real systems. A computer table is just furniture.
Which of the following is NOT a Data MINING technique?
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Correct answer: (D) Evaluation
Explanation
Link analysis, database segmentation (clustering) and predictive modelling are data mining techniques. Evaluation is a general step, not a mining technique.
What is the cardinality of Relation having 500 tuples and 50 attribute?
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Correct answer: (A) 500
Explanation
Cardinality is the number of tuples (rows) in a relation, so it is 500. The number of attributes (50) is the degree.
How many rule does Dr. E.F. codd provides which qualify quality a database as a RDBMS?
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Correct answer: (C) 12
Explanation
E.F. Codd gave 12 rules, numbered 1-12 with an extra Rule 0 (the foundation rule), that a DBMS must satisfy to be called fully relational.
Which of the following is a type of connection trap in Entity relationship model?
I. Fan-traps
II. Chasm-traps
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Correct answer: (C) Both I and II
Explanation
Fan traps and chasm traps are the two kinds of connection trap in ER modelling. A fan trap gives ambiguous paths between entities, and a chasm trap gives a missing path.
Which of the following symbol represent one to one cardinality relationship in Entity relationship diagram?
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Correct answer: (B) ─|─ (a line with a single bar)
Explanation
In crow's-foot notation, a single bar means "one". A line with a single bar marks a one-to-one link. A crow's foot means "many", and a circle means "zero" (optional).
Which of the following is NOT an approach of database design in database management system?
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Correct answer: (D) UP-down approach
Explanation
The recognised database design approaches are top-down, bottom-up, inside-out and mixed. There is no "up-down" approach.
Which of the following is an Aggregate operator in structured Query Language?
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Correct answer: (D) Count
Explanation
COUNT is an aggregate function: it returns one value computed over a set of rows. MINUS, INTERSECT and UNION are set operators.
Which attribute in HTML table tag defines the number of columns in a column group?
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Correct answer: (D) Span
Explanation
The span attribute of <colgroup> or <col> sets how many columns the group covers. Colspan and rowspan are used on table cells (td or th).
Which is the value of f'(x) at x = 4 from the following table of values?
x | 1 | 2 | 3 | 4
f(x) | 20 | 22 | 27 | 34
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Correct answer: (D) 9.5
Explanation
Note: the answer key gives (D) 9.5, but with this table Newton's backward formula gives f′(4) = ∇f + ∇²f/2 + ∇³f/3 = 7 + 2/2 − 1/3 ≈ 7.67. No option matches, so the table is probably misprinted.
Which of the following is a invalid relational operator in Java?
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Correct answer: (B) =>
Explanation
Java's relational operators are <, >, <=, >=, == and !=. "=>" is not a valid operator in Java.
What is the description of append keyword of visual Basic net keyword?
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Correct answer: (C) Used as a symbolic constant in the fileopen function
Explanation
In VB.NET, Append is used as a symbolic constant (OpenMode.Append) in the FileOpen function, to open a file and add data at its end.
The following keys 22, 28, 23, 12 and 13 are inserted into initially empty hash table of length 9 using open addressing with hash function h(k) = k mod 9 and linear probing. At what index key 13 is inserted?
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Correct answer: (C) 6
Explanation
22→4, 28→1, 23→5, 12→3. 13 mod 9 = 4 is taken, so linear probing tries 5 (taken), then 6, which is free. So 13 goes to index 6.
Which gate is represented by the following truth table?
A | B | C | Output
0 | 0 | 0 | 1
0 | 0 | 1 | 1
0 | 1 | 0 | 1
0 | 1 | 1 | 1
1 | 0 | 0 | 1
1 | 0 | 1 | 1
1 | 1 | 0 | 1
1 | 1 | 1 | 0
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Correct answer: (B) NAND
Explanation
The output is 0 only when all inputs are 1 and 1 otherwise, which is (ABC)', the NAND function.
How to use these DSSSB TGT / PGT Computer Science questions
Every question here was asked in a real DSSSB TGT / PGT paper; the paper and shift are shown on the card, and the number opens the question on its own page. Try each one before tapping Show answer, then attempt the full DSSSB TGT / PGT papers as timed tests to check your speed under exam conditions.