Discussion
WHERE construct in SQL is equivalent to following relational algebra operator ?
Answer: B
WHERE corresponds to selection, \(\sigma\).
The WHERE clause picks out the rows (tuples) that satisfy a condition, which is exactly the selection operator: SELECT * FROM R WHERE C is \(\sigma_{C}(R)\).
\(\Pi\) (projection) corresponds to the column list after SELECT. \(\times\) (Cartesian product) corresponds to listing several tables in FROM, and \(\bowtie\) (join) to JOIN ... ON, which is a selection applied to a product.
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