Invisible wrote:
>>> (Anybody have any clue how the relational calculus is different from 
>>> the relational algebra??)
>>
>> Yes.
> 
> Care to explain?

It's kind of like the difference between functional and procedural.

In the calculus, you say "give me a table with the name, salary, and hire 
date from table X and table Y where X.name=Y.name and salary < 500"

In the algebra, you say "join table X and Y, and from that select the ones 
where the names are the same, and from that select the ones where the salary 
is < 500, and from that project over name, salary, and hire."

Think of SQL compared to something like

(((X join Y) select {salary < 500})
     select {X.name = Y.name}) project [name,salary,hire]

Only select, project, and join are defined in the algebra. There's no 
"exists" and such.

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

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