SELECT operation in SQL is equivalent to
2015
SELECT operation in SQL is equivalent to
- A.
the selection operation in relational algebra
- B.
the selection operation in relational algebra, except that SELECT in SQL retains duplicates
- C.
the projection operation in relational algebra
- D.
the projection operation in relational algebra, except that SELECT in SQL retains duplicates
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Correct answer: D
Short answer: SELECT in SQL corresponds to the projection operation in relational algebra, except that SQL retains duplicate rows by default (use DISTINCT to remove duplicates).
Projection (relational algebra) = choosing columns (attributes). Example: SELECT name FROM Students corresponds to projecting the name attribute.
Difference: relational-algebra projection removes duplicate rows; SQL's SELECT keeps duplicates unless you use SELECT DISTINCT.
Note: The selection operation in relational algebra corresponds to SQL's WHERE clause (it filters rows), not to SELECT.
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