Comment by ben509
7 years ago
> In situations where EdgeDB cannot infer the type of an empty set [2]
Why not bottom, or are containers not covariant? I'm worried that we're not clear about the difference between variables and values.
> Strictly speaking, EdgeQL sets are multisets [1]
Like nulls, this is another broken aspects of SQL.
Maybe you can address these concerns, but I'm skeptical that it's relational:
* It conflates types with relation variables
* It's using links rather than foreign key constraints
* It doesn't seem like the user can even specify a candidate key
* Which is why the "id" field is magical and special
* Constraints only seem to apply to scalars
The reason SQL has been successful is that tables are dead simple to understand, and you're throwing that out. This feels more like a graph database.
[1]: https://edgedb.com/docs/edgeql/overview#type-system [2]: https://edgedb.com/docs/edgeql/expressions/overview#set-cons...
>> Why not bottom, or are containers not covariant? I'm worried that we're not clear about the difference between variables and values.
Yes, `{}` is inferred as `anytype`, but we chose to restrict its use in output for interoperability reasons: the output of a query must be of a concrete, known type.
>> Strictly speaking, EdgeQL sets are multisets [1] > Like nulls, this is another broken aspects of SQL.
From the purity standpoint, yes, but in practice, duplicate values are either expected, or too expensive to eliminate. That said there is a `DISTINCT` [1] aggregate.
> * It conflates types with relation variables
Not exactly. We do use the same symbol to denote a type, and a relation that it represents, but the context of which is which is always clear (i.e. Foo in a cast expression is always a type), but Foo in a regular expression is always a relvar.
> * It's using links rather than foreign key constraints
Links are an abstraction over a foreign key. In the vast majority of cases foreign keys are implemented as 'some_id' -> 'id' anyway. If you want a custom foreign key, you can set an expression constraint on a property or a link.
> * It doesn't seem like the user can even specify a candidate key
type Foo { constraint exclusive on ((.name, .last_name)) }
> * Which is why the "id" field is magical and special
See RM proscription 15 in the Third Manifesto [2]
> * Constraints only seem to apply to scalars
They aren't, see above.
[1] https://edgedb.com/docs/edgeql/funcops/set#operator::DISTINC... [2] https://www.dcs.warwick.ac.uk/~hugh/TTM/DTATRM.pdf
Thanks for the clarifications!