GATE Databases 5

Question 1

Which of the following correctly describes a 'lossless join decomposition'?

Accepted Answer

The natural join of the decomposed relations exactly reconstructs the original relation

Answer

A lossless join decomposition guarantees that joining the parts back on common attributes yields exactly the original relation with no spurious tuples.

Question 2

In a B-tree (not B+ tree) of order m, the maximum number of keys in a node is:

Accepted Answer

m - 1

Answer

A B-tree node of order m holds at most m children and therefore at most m-1 keys.

Question 3

Which relational algebra expression represents the SQL: SELECT A FROM R WHERE B = 5?

Accepted Answer

π_A(σ_{B=5}(R))

Answer

First apply selection to filter rows (σ_{B=5}), then apply projection to keep only column A (π_A).

Question 4

The concept of 'data independence' in DBMS most directly refers to:

Accepted Answer

Ability to change the schema at one level without affecting higher levels

Answer

Data independence allows changes to physical or logical schema without requiring application code changes, enabled by the three-level ANSI/SPARC architecture.

Question 5

Which aggregate function in SQL ignores NULL values by default?

Accepted Answer

SUM, AVG, MIN, MAX but not COUNT(*)

Answer

COUNT(*) counts all rows including NULLs; SUM, AVG, MIN, MAX, and COUNT(column) all skip NULL values.

(GATE) Graduate Aptitude Test in Engineering Practice Test

(GATE) Graduate Aptitude Test in Engineering Practice Test

GATE Databases 5