GATE CS 1999 Q2.25 — Tuple Calculus and SQL

Let us analyze each option to determine its correctness:

• Option A is incorrect: By default, SQL queries use multiset (bag) semantics and do not automatically eliminate duplicates. To eliminate duplicate rows from the query result, the DISTINCT keyword must be explicitly specified.
• Option B is incorrect: Indexes are optional physical database structures used to optimize query performance. SQL queries execute perfectly fine without indexes, typically using sequential table scans.
• Option C is incorrect: In any relational database management system (RDBMS), all attribute (column) names within a single relation (table) must be unique to prevent ambiguity.

Since all the statements A, B, and C are incorrect, the correct option is D.