0 0 votes Let R1(a,b) = {(2,3),(3,2),(2,4),(2,5)},R2={(2,2),(3,3)} then find $\Pi_{AB(R1)}/\Pi_{B}(\sigma _{c>3}(R2))$ Databases databases relational-algebra + – Anjan 1.3k views answer comment Share Follow Print See all 6 Comments 6 6 Comments reply Rupendra Choudhary commented Nov 9, 2017 reply Follow flag Hello Anjan , type your question properly. you didn't provide attribute set for relation R2. i'm supposing R2(B,C) and no c<3 so it will return nothing and hence o/p of query will return nothing.0 tuple 1 1 replyShare joshi_nitish commented Nov 10, 2017 reply Follow flag is it R2(B,C) or R2(C,B)....though it will not affect answer here, but provide it. here answer will be, πAB(R1) / πB(σc>3(R2)) = {2,3} because bolded query will return NULL, which will result in projection of all the distinct values of R1(A). 1 1 replyShare Anu007 commented Nov 10, 2017 reply Follow flag yes πAB(R1) / empty = πAB(R1) 0 0 replyShare joshi_nitish commented Nov 10, 2017 reply Follow flag it should be, πAB(R1) / empty = πA(R1) // for above qsn 1 1 replyShare Sukannya commented Nov 10, 2017 reply Follow flag What are R2's attributes? 0 0 replyShare pradeepchaudhary commented Mar 24, 2018 reply Follow flag why only (A) attribute of R1 is printed? 0 0 replyShare Please log in or register to add a comment.
