phillipleblanc opened a new issue, #13822:
URL: https://github.com/apache/datafusion/issues/13822
### Is your feature request related to a problem or challenge?
Currently DataFusion only support queries with 3-levels of nesting, i.e.
`SELECT * FROM catalog.schema.table`. Many catalog providers (i.e. Iceberg)
allow any arbitrary level of nesting, i.e.:
```bash
.
├── benchmarks
│ └── tpcds
│ ├── foo
│ └── bar
├── spice
│ ├── tpch
│ │ ├── orders
│ │ └── customers
│ ├── info
│ └── extra
│ └── tpch_orders_metadata
└── one
└── two
└── three
└── four
└── five
```
Attempting to represent this in DataFusion is tricky and several of the
alternatives I considered (see below) are poor UX.
### Describe the solution you'd like
I would like to be able to write a catalog provider that allows users to
select any of the tables in the Iceberg catalog with a natural dot separated
syntax. `sqlparser-rs` already supports parsing this, creating an `ObjectName`
which is a `Vec<Ident>`.
There is a function in DataFusion
[`idents_to_table_reference`](https://github.com/apache/datafusion/blob/main/datafusion/sql/src/planner.rs#L668)
that is responsible for transforming the `Vec<Ident>` into a `TableReference`.
Its current implement looks like:
```rust
pub(crate) fn idents_to_table_reference(
idents: Vec<Ident>,
enable_normalization: bool,
) -> Result<TableReference> {
let mut taker = IdentTaker::new(idents, enable_normalization);
match taker.len() {
1 => {
let table = taker.take();
Ok(TableReference::bare(table))
}
2 => {
let table = taker.take();
let schema = taker.take();
Ok(TableReference::partial(schema, table))
}
3 => {
let table = taker.take();
let schema = taker.take();
let catalog = taker.take();
Ok(TableReference::full(catalog, schema, table))
}
_ => plan_err!(
"Unsupported compound identifier '{}'. Expected 1, 2 or 3 parts,
got {}",
taker,
taker.len()
),
}
}
```
Instead of erroring on >3 idents, I propose that we concatenate all of the
"middle" namespaces into the `schema` part:
```rust
// This won't compile as is, but demonstrates the idea
_ => {
// Concatenate all of the middle identifiers with a dot and put
into the "schema" field
let table = taker.take(enable_normalization);
let schema = idents
.iter()
.skip(1)
.take(idents.len() - 2)
.map(|ident| {
IdentNormalizer::new(enable_normalization).normalize(ident.clone())
})
.collect::<Vec<_>>()
.join(".");
let catalog = taker.take(enable_normalization);
Ok(TableReference::full(catalog, schema, table))
}
```
That would allow us to do `SELECT * FROM one.two.three.four.five` and have
it be converted into a DF TableReference with:
`catalog`: one
`schema`: two.three.four
`table`: five
And any catalog provider implementations can know to create "schemas" to
match this format to support arbitrarily nested namespaces.
### Describe alternatives you've considered
I've considered in my implementation when integrating with a catalog
provider to concatenate the middle namespaces with a `_` in the schema part so
that `SELECT * FROM one.two.three.four.five` would become `SELECT * FROM
one.two_three_four.five`.
I've also considered concatenating the middle namspaces with `.` and not
changing DataFusion, but that would require doing `SELECT * FROM
one."two.three.four".five` which is also not an ideal UX.
Another alternative if we didn't want this to be the default, is to allow
users to customize the behavior of the `object_name_to_table_reference`
function somehow.
### Additional context
_No response_
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