Re: "Aggregate" operators

On 25/04/2017 11:04, Norbert_Paul wrote:
> Erwin wrote:
>> Looking for a *formal* definition of the term "aggregate" operator.
>>
>> The term is quite familiar and the one in common use to denote SQL
>> operators such as MIN, MAX,
>> AVG that occur exclusively in connection with some GROUP BY.
>>
>> However, "occur exclusively in connection with SQL GROUP BY" is rather
>> non-mathematical as a
>> formal definition and so, is anyone around here aware of something
>> more rigorous as a
>> *definition* of when some operator is or is not an "aggregate" operator ?
>
> Formally "GROUP BY a, b,..." is a partition of the table, where "table"
> is informal for
> "set of tuples". [...]

Note that SQL has bag semantics, but aggregate functions may be formally defined wrt set semantics. In the context of the Relational model, probably the latter is more natural.

Nicola Received on Tue Apr 25 2017 - 14:22:24 CEST