ER and Relational Models (original) (raw)

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

• An attribute of an entity can have more than one value
• An attribute of an entity can be composite
• In a row of a relational table, an attribute can have more than one value
• In a row of a relational table, an attribute can have exactly one value or a NULL value

Suppose (

A

, B) and (

C

,D) are two relation schemas. Let r1 and r2 be the corresponding relation instances. B is a foreign key that refers to C in r2. If data in r1 and r2 satisfy referential integrity constraints, which of the following is ALWAYS TRUE?

Consider the following relations A, B, C. How many tuples does the result of the following relational algebra expression contain? Assume that the schema of A U B is the same as that of A.

**Table A
Id Name Age

12 Arun 60
15 Shreya 24
99 Rohit 11

**Table B
Id Name Age

15 Shreya 24
25 Hari 40
98 Rohit 20
99 Rohit 11

**Table C
Id Phone Area

10 2200 02
99 2100 01

Consider a relational table r with sufficient number of records, having attributes A1, A2,…, An and let 1 <= p <= n. Two queries Q1 and Q2 are given below.

The database can be configured to do ordered indexing on Ap or hashing on Ap. Which of the following statements is TRUE?

• Ordered indexing will always outperform hashing for both queries
• Hashing will always outperform ordered indexing for both queries
• Hashing will outperform ordered indexing on Q1, but not on Q2
• Hashing will outperform ordered indexing on Q2, but not on Q1.

Which commands are used to control access over objects in relational database?

If D1, D2...Dn are domains in a relational model, then the relation is a table, which is a subset of

The join operation can be defined as

• a cartesian product of two relations followed by a selection
• a cartesian product of two relations
• a union of two relations followed by cartesian product of the two relations

The 'command' used to change contents of one database using the contents of another database by linking them on a common key field?

For a weak entity set to be meaningful, it must be associated with another entity set in combination with some of their attribute values, is called as:

Drop Table cannot be used to drop a Table referenced by __________ constraint. (a)Primary key (b)Sub key (c)Super key (d)Foreign key

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