Consider the following SQL query select distinct al, a2,........., an from r1, r2,........, rm where P For an arbitrary predicate P, this query is equivalent to which of the following relational algebra expressions ? A TEX prod a 1 ,a 2 ,...a n sigma rho (r 1 times r 2 times r 3 .... times r m ) TEX B TEX prod a 1 ,a 2 ,...a n sigma rho (r 1 bowtie r 2 bowtie r 3 .... bowtie r m ) TEX C TEX prod a 1 ,a 2 ,...a n sigma rho (r 1 cup r 2 cup r 3 .... cup r m ) TEX D TEX prod a 1 ,a 2 ,...a n sigma rho (r 1 cap r 2 cap r 3 .... cap r m ) TEX

GATE | GATE-CS-2003 | Question 30

Last Updated : 14 Feb, 2018

Consider the following SQL query

select distinct al, a2,........., an
from r1, r2,........, rm
where P

For an arbitrary predicate P, this query is equivalent to which of the following relational algebra expressions ? A: $\prod_{a_{1},a_{2},...a_{n}}\sigma_{\rho} (r_{1}\times r_{2}\times r_{3}....\times r_{m})$ B: $\prod_{a_{1},a_{2},...a_{n}}\sigma_{\rho} (r_{1}\bowtie r_{2}\bowtie r_{3}....\bowtie r_{m})$ C: $\prod_{a_{1},a_{2},...a_{n}}\sigma_{\rho} (r_{1}\cup r_{2}\cup r_{3}....\cup r_{m})$ D: $\prod_{a_{1},a_{2},...a_{n}}\sigma_{\rho} (r_{1}\cap r_{2}\cap r_{3}....\cap r_{m})$ (A) A (B) B (C) C (D) D

Answer: (A)

Explanation:
Cross product (x) combines the tuples of one relation with all the tuples of the other relation. Thus, tuples of relation r1, r2 …. rn are combined.
Select operator $\sigma$ is used to select resultant tuples.
Projection operator $\prod_{a_{1},a_{2},...a_{n}}$ is used to select a subset of attributes from the resultant tuples by specifying the names of the attributes. So attributes a1, a2, an are projected from the resultant tuples.

Thus, option (A) is correct.

Please comment below if you find anything wrong in the above post.

Quiz of this Question

Suggest improvement

GATE | GATE-CS-2003 | Question 88

GATE | GATE-CS-2003 | Question 31

Share your thoughts in the comments

GATE | GATE-CS-2003 | Question 30

Please Login to comment...

Similar Reads

What kind of Experience do you want to share?