Re: Relational Algebra Expression

On Feb 9, 4:47 pm, Bob Badour <bbad...@xxxxxxxxxxxxxxxx> wrote:
gamehack wrote:
[snip]
What I'm trying to do is extract all the years where we have more than
1 relation for the year. For the sample table, we need to get:
1999
2001

I tried to do in a couple of ways but I couldn't. I tried using a
projection on Year so that I can remove duplicates but then I can't
just use difference because the new relations are not compatible. Any
hints are greatly appreciated.

Equijoin on year and inequality theta-join on name project on year.

Hi,

I can't really understand what this means - can you bracket it so I
can see the results of each operation?

Thanks very much,
g
.

Relevant Pages

  • Re: Relational Algebra Expression
    ... projection on Year so that I can remove duplicates but then I can't ... I would use "rename all but year prepending ...
    (comp.databases.theory)
  • Re: Relational Algebra Expression
    ... projection on Year so that I can remove duplicates but then I can't ... It would be just peachy keen if it didn't look so much like it had a bug then. ...
    (comp.databases.theory)
  • Re: Relational Algebra Expression
    ... projection on Year so that I can remove duplicates but then I can't ... It would be just peachy keen if it didn't have a bug. ...
    (comp.databases.theory)
  • Re: an electronish puzzle
    ... >What is truly pathetic is your projection of your own ... >miserable outlook into a fantasy about what was a ...
    (sci.electronics.design)
  • Re: Relational Algebra Expression
    ... gamehack wrote: ... projection on Year so that I can remove duplicates but then I can't ...
    (comp.databases.theory)