Actually, SQL does a mixture of both relational calculus and relational
algebra,
but not necessarily all of either.
Seeing the algebra is fairly straightforward, eg the UNION or WHERE etc.
An example of the calculus is seen in SELECT...FROM... involving a JOIN, for
example:
SELECT person.name, person.age, department.deptname
FROM people person
INNER JOIN departments department ON (department.deptid = person.deptid);
In SQL, each named source in the FROM clause is effectively a FORALL (or
something) over a set (eg people) which has an associated variable which has
the
value of a set element in turn (eg person).
Its commonly misunderstood that declaring an alias in FROM is aliasing the
whole
table, but it isn't, rather it is aliasing a single record of the table; if you
don't have an explicit alias, the record variable defaults to the same name as
the table. My above example should make more clear what's going on.
-- Darren Duncan
On 2015-06-15 5:46 PM, Christopher Vance wrote:
> With a relational model you have a choice between relational calculus or
> relational algebra. SQL does one of them.
>
> I have used a language which did the other, long ago in a land far away.
>
> On Tue, Jun 16, 2015 at 9:56 AM, <david at andl.org> wrote:
>
>>>>> I think the best database language should reflect how earthlings think
>> about the data, and the best computer programming language would reflect
>> easily the result we want get from them.
>>
>> Care to expand on that?
>>
>> I'm developing a new database language: Andl. My starting point has been
>> the
>> relational model, Codd-Date-Darwen and The Third Manifesto. My (only)
>> competitor seems to be SQL, which has a 40+ year lead. Nothing like a
>> challenge!
>>
>> The question is: what should a database language do? Andl can already match
>> or surpass SQL on database programming tasks, but is that interesting
>> enough?
>>
>> What would make a database programming better, or best?
>>
>> Regards
>> David M Bennett FACS
>>
>> Andl - A New Database Language - andl.org
