GATE CSE 2015 Set 1 | Question: 7

Question

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

Answer 1

Option D is correct because SELECT operation in SQL is equivalent to The projection operation in relational algebra, except that SELECT in SQL retains duplicates but projection gives only distinct. 

Comments

any source/material for explanation!

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The below link has a ppt to explain this answer

http://courses.cs.vt.edu/~cs4604/Fall09/lectures/lecture-03-intro-sql-relational-algebra.pdf

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Selection in relational algebra select rows and projection in RA select columns. Select operation in SQL selects columns but duplicates values are retained in SQL.

Answer 2

The SELECT operation in SQL is equivalent to the selection operation in relational algebra.

The SELECT operation in SQL is used to retrieve specific columns and rows from a table in a relational database. This operation is similar to the selection operation in relational algebra, which is used to select a subset of rows from a relation based on a specified condition.

Both SELECT in SQL and selection in relational algebra retain duplicate rows when they are selected, and the SELECT operation in SQL does not eliminate duplicates.

The projection operation in relational algebra is used to select a subset of columns from a relation, which is not the same as the SELECT operation in SQL.