Which of the following is TRUE?

Question

BlackTom AI · Accepted Answer

The given data for this question is incomplete: there are no answer options provided to analyze, and only a single item appears in the 'answer' field. This means we cannot perform a option-by-option evaluation as requested.

What is present suggests a potential true statement to consider: 'SELECT DISTINCT is the SQL equivalent of Projection (Pi) in Relational Algebra.' To reason about this claim in isolation:
- In relational algebra, the projection operation Pi_{attributes}(R) selects specific attributes from a relation R. By the standard set-theoretic foundation of relational algebra, duplicates are not kept; the result of a projection is a set of tuples with only the chosen attributes, with duplicates eliminated.
- In SQL, SELECT can return duplicates unless the DISTINCT keyword is used. Therefore, SELECT DISTINCT indeed corresponds to projection with duplicate elimination, aligning with the set semantics of Pi in relational algebra. However, plain SELECT without DISTINCT does not enforce duplicate elimination, so it is not equivalent to Pi in the strict sense.
- If the question intended to equate projection with the use of DISTINCT, then the statement would be true under the common interpretation that projection implies removing duplicate rows for the projected attributes. If the statement intended to claim that any SELECT (without DISTINCT) is equivalent to Pi, that would be false.

Given there are no explicit answer choices to assess, no option-by-option critique can be provided. If you can supply the full set of options, I can evaluate each one and explain why it is true or false with varied reasoning.

Note: In typical educational materials, the standard takeaway is that SELECT DISTINCT corresponds to projection with duplicate elimination (the relational algebra Pi operation), while Pi itself embodies the concept of selecting specific attributes, independent of how duplicates are handled in SQL.

INFO20003_2025_SM2 Practice Exam Quiz

Which of the following is TRUE?

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