ER Diagram to Relational Model MCQs: 12 Solved Questions

Before counting tables, identify cardinality, participation, weak entities, multivalued attributes and relationship attributes. The usual error is treating every diamond as a table.

Sketch relations and mark primary and foreign keys before checking the options. CS Fundamentals for Placements connects this topic to wider DBMS.

ER-to-relational mapping rules to use before the MCQs

Total participation affects nullability or merging, not entity existence. ER Model to Relational Mapping for GATE gives the full method.

Map Department(DeptID, DeptName), Student(StudentID, StudentName, {Phone}) and Course(CourseID, CourseTitle). Department-Student is 1:N; Student-Course is M:N through Enrols with Grade and EnrolledOn.

1. DEPARTMENT(DeptID PK, DeptName): (D10, CSE).

2. STUDENT(StudentID PK, StudentName, DeptID FK): (101, Asha, D10) and (102, Rohan, D10). DeptID absorbs 1:N; no sixth table is needed.

3. COURSE(CourseID PK, CourseTitle): (DB201, Database Systems) and (CN202, Computer Networks).

4. ENROLMENT(StudentID FK, CourseID FK, Grade, EnrolledOn, PK(StudentID, CourseID)): (101, DB201, A, 2026-07-01), (101, CN202, B+, 2026-07-02) and (102, DB201, A-, 2026-07-01).

5. STUDENT_PHONE(StudentID FK, Phone, PK(StudentID, Phone)): (101, 9876501111), (101, 9876502222) and (102, 9876503333).

The count is 3 entity relations + 1 M:N bridge + 1 multivalued-attribute relation = 5.

MCQs 1-3: relationship types, participation and bridge relations

Question 1

TPSC 2025, Assistant Programmer.

Which of the following is a type of relationship in a relational database ?

• A. One-to-one

• B. One-to-many

• C. Many-to-many

• D. All of the above

Answer: D. All of the above. Foreign keys map 1:1 and 1:N; M:N needs a bridge.

Question 2

Coal India 2017.

Which of the following is used to specify whether the existence of an entity depends on its being related to another entity via the relationship type?

• A. Entity integrity constraint

• B. Foreign key constraint

• C. Cardinality ratio

• D. Participation constraint

Answer: D. Participation constraint. Cardinality gives counts; participation says whether involvement is mandatory.

Question 3

LTI Mindtree 2025.

Which of the following results in each related entity set having its own schema, along with an additional schema being created for the relationship set?

• A. A many-to-many relationship set

• B. A multivalued attribute of an entity set

• C. A one-to-many relationship set

• D. None of the mentioned

Answer: A. A many-to-many relationship set. Student and Course remain; ENROLMENT(StudentID, CourseID, Grade, EnrolledOn) represents their matches.

MCQs 4-6: multivalued attributes, relationship merging and 3NF counts

Question 4

CoCubes 2024.

In which of the following, a separate schema is created consisting of that attribute and the primary key of the entity set.

• A. A many-to-many relationship set

• B. A multivalued attribute of an entity set

• C. A one-to-many relationship set

• D. All of the mentioned

Answer: B. A multivalued attribute of an entity set. STUDENT_PHONE(StudentID, Phone) keeps values atomic; both columns form the key.

Question 5

GATE 2017, Set 2.

An ER model of a database consists of entity types A and B. These are connected by a relationship R which does not have its own attribute. Under which one of the following conditions, can the relational table for R be merged with that of A?

• A. Relationship R is one-to-many and the participation of A in R is total

• B. Relationship R is one-to-many and the participation of A in R is partial

• C. Relationship R is many-to-one and the participation of A in R is total

• D. Relationship R is many-to-one and the participation of A in R is partial

Answer: C. A carries B's foreign key, and total participation permits merging.

Question 6

GATE 2004, Information Technology.

Consider the following entity relationship diagram (ERD), where two entities E1 and E2 have a relation R of cardinality 1 : m.

The attributes of E1 are A11, A12 and A13 where A11 is the key attribute. The attributes of E2 are A21, A22 and A23 where A21 is the key attribute and A23 is a multi-valued attribute. Relation R does not have any attribute. A relational database containing minimum number of tables with each table satisfying the requirements of the third normal form (3NF) is designed from the above ERD. The number of tables in the database is

• A. 2

• B. 3

• C. 5

• D. 4

Answer: B. 3. Create E1 and E2, with A11 in E2 as a foreign key. Add E2_A23(A21, A23) for A23. Thus 2 + 0 + 1 = 3; R adds nothing.

MCQs 7-9: why a 1:N plus M:N pattern gives three tables

For each count, model the 1:N relationship with a foreign key and the M:N relationship with a bridge.

Question 7

ISRO 2025.

Let A and B be two entities in an E-R diagram, each having only simple single-valued attributes. R1 and R2 are two relationships between A and B. R1 is one-to-many from A to B, and R2 is many-to-many from A to B. What is the minimum number of tables required to represent A, B, R1 and R2 in the relational model?

• A. 4

• B. 2

• C. 6

• D. 3

Answer: D. 3. A and B give two relations. R1 becomes B's foreign key; R2 adds a bridge: 2 + 0 + 1 = 3.

Question 8

GATE 2005.

Let E₁ and E₂ be two entities in an E/R diagram with simple single-valued attributes.

R₁ and R₂ are two relationships between E₁ and E₂, where R₁ is one-to-many and R₂ is many-to-many.

R₁ and R₂ do not have any attributes of their own.

What is the minimum number of tables required to represent this situation in the relational model?

• A. 2

• B. 3

• C. 4

• D. 5

Answer: B. 3. E₁ and E₂ give two relations. R₁ becomes a foreign key; R₂ needs a bridge.

Question 9

UGC NET January 2017.

Let M and N be two entities in an E-R diagram with simple single value attributes. R1 and R2 are two relationship between M and N, where as

R1 is one-to-many and R2 is many-to-many.

The minimum number of tables required to represent M, N, R1 and R2 in the relational model are _______.

• A. 4

• B. 6

• C. 7

• D. 3

Answer: D. 3. M and N give two relations, R1 a foreign key, and R2 a bridge.

MCQs 10-12: weak entities, relationship attributes and multivalued mappings

Question 10

GATE 2008.

Consider the following ER diagram.

The minimum number of tables needed to represent M, N, P, R1, R2 is

• A. 2

• B. 3

• C. 4

• D. 5

Answer: B. 3. Create M, P and weak N. P's key enters M and combines with N1 in N; neither relationship adds a table.

Question 11

ISRO 2015.

Consider the following Relationship Entity Diagram(ERD)

Which of the following possible relations will not hold if the above ERD is mapped into a relation model?

• A. Person (NID, Name)

• B. Qualification (NID, ExamID, QualifiedDate)

• C. Exam (ExamID, NID, ExamName)

• D. Exam (ExamID, ExamName)

Answer: C. Exam (ExamID, NID, ExamName) will not hold. The M:N association belongs in Qualification, not Exam.

Question 12

TPSC 2026.

When converting an E-R diagram to a relational schema, how is a multivalued attribute typically represented in the relational model?

• A. As a composite attribute

• B. As a nullable column in the same table

• C. As an attribute with CHECK constraints

• D. As a separate relation with a foreign key

Answer: D. As a separate relation with a foreign key. A multivalued attribute can contain several values for one entity row, so placing it in one column would violate first normal form. Create a separate relation containing the owner's key as a foreign key and the attribute value; together they usually form the relation's key.

The five ER-mapping traps these questions expose

Count entities, then add M:N or n-ary relationships and multivalued attributes. Check 1:1 and 1:N for foreign-key absorption. Participation affects nullability.

ER diagram to relational model MCQs: the next practice step

Redo Questions 5, 6, 10 and 11 without options. Write schemas, mark primary and foreign keys, then verify the counts.

Use Attribute Closure and Candidate Keys for GATE to identify keys after deriving relations. GATE Guidance by Sanchit Sir provides a sequenced DBMS route; CS Fundamentals for Placements by Sanchit Sir provides broader placement coverage.

Entities give base relations. M:N and multivalued attributes add relations. 1:N usually becomes a foreign key on the many side.