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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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