mustafasrepo commented on code in PR #7040:
URL: https://github.com/apache/arrow-datafusion/pull/7040#discussion_r1270846585
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datafusion/core/src/datasource/default_table_source.rs:
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@@ -52,6 +54,11 @@ impl TableSource for DefaultTableSource {
self.table_provider.schema()
}
+ /// Get a reference to primary key indices, if a primary key exists.
+ fn primary_keys(&self) -> Option<&[usize]> {
Review Comment:
> Would it be possible to make this API more general? Specifically, there
are several kinds of keys that a table might have so special casing primary key
will make supporting others harder in the future
>
> Single column primary key
>
> ```sql
> create table t (
> x int primary key,
> y int,
> z int)
> ```
>
> Unique (like primary key, but can be null)
>
> ```sql
> create table t (
> x int unique,
> y int,
> z int)
> ```
>
> Multi column primary key
>
> ```sql
> create table t (
> x int,
> y int,
> z int,
> primary key (x, y)
> )
> ```
>
> Foreign key:
>
> ```sql
> create table t (
> x int,
> y int,
> z int,
> foreign key (x) references other_table(a)
> )
> ```
>
> Perhaps we could make it this more general someting like
>
> ```rust
> pub enum Constraints {
> // columns together form a primary key (are unique and not null)
> PrimaryKey(Vec<usize>),
> // columns together form a unique key
> Unique(Vec<usize>),
> // More constraint types to come as we add additional support
> }
> ```
>
> fn constraints(&self) -> Vec { ... }
Thanks @alamb for your feedback. Other than this suggestion, I have
implemented all of your suggestions. With, your suggestions functional
dependencies are now better encapsulated. Most of functionality is moved to the
methods.
`FunctionalDependecies` now has a method `new_from_primary_keys`. All of the
mapping between primary key and functioanal dependency occur, with this method.
Hopefully, when we change this API, changing `new_from_primary_keys` and doing
necessary mapping will be enough. If it is OK with you, I can change this API
in following PRs.
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