here it says Selection and cross product Cross prod开发者_JS百科uct is the costliest operator to evaluate. If the input relations have N and M rows, the result will contain NM rows. Therefore it is
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I\'m stuck at the query below where i\'ll need to list out two attributes from different tables. Is there a simpler way to write the above query?
I have several SQL queries written that I want to convert to relational algebra.However, some of the queries use aggregate operators and I don\'t know how to convert them.Notably they use COUNT and GR
If I have a schema say R={A,B,C,D} and functional depen开发者_如何学Cdencies say {B->C, D->A} will my set of candidate keys be {B,D} or {BD}?If B were a candidate key, you\'d have to be able to
I\'m looking for a clear, basic explanation of the concept of theta join in relational algebra and perhaps an example (using SQL perhaps) to illustrate its usage.
This is probably a silly question however, is there a simple way of doing 开发者_JAVA百科antijoins of collections in Groovy?
This is not homework but has a direct relation to my homework.In other words, I need to know this information to be able to do my homework.
This topic is somewhat related to this question. There my answer was motivated by the assumption that SQL is necessary to access data in every database I know.
What does AREL stand f开发者_开发技巧or? I couldn\'t find what\'s the meaning of this acronym anywhere.This?https://github.com/nkallen/arel\"A RELational algebra\"
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