milenkovicm commented on code in PR #17859:
URL: https://github.com/apache/datafusion/pull/17859#discussion_r2395922718
##########
datafusion/core/src/execution/context/mod.rs:
##########
@@ -1786,28 +1786,56 @@ impl From<SessionContext> for SessionStateBuilder {
/// A planner used to add extensions to DataFusion logical and physical plans.
#[async_trait]
pub trait QueryPlanner: Debug {
- /// Given a `LogicalPlan`, create an [`ExecutionPlan`] suitable for
execution
+ /// Given a [`LogicalPlan`], create an [`ExecutionPlan`] suitable for
execution
async fn create_physical_plan(
&self,
logical_plan: &LogicalPlan,
session_state: &SessionState,
) -> Result<Arc<dyn ExecutionPlan>>;
}
-/// A pluggable interface to handle `CREATE FUNCTION` statements
-/// and interact with [SessionState] to registers new udf, udaf or udwf.
+/// Interface for handling `CREATE FUNCTION` statements and interacting with
+/// [SessionState] to create and register functions ([`ScalarUDF`],
+/// [`AggregateUDF`], [`WindowUDF`], and [`TableFunctionImpl`]) dynamically.
+///
+/// Implement this trait to create user-defined functions in a custom way, such
+/// as loading from external libraries or defining them programmatically.
+/// DataFusion will parse `CREATE FUNCTION` statements into [`CreateFunction`]
+/// structs and pass them to the [`create`](Self::create) method.
+///
+/// Note there is no default implementation of this trait provided in
DataFusion,
+/// because the implementation and requirements vary widely. Please see
+/// [function_factory example] for a reference implementation.
+///
+/// [function_factory example]:
https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/function_factory.rs
+///
+/// # Examples of syntax that can be supported
+///
+/// ```sql
+/// CREATE FUNCTION f1(BIGINT)
+/// RETURNS BIGINT
+/// RETURN $1 + 1;
Review Comment:
one note, not related to this PR, it would be great if we could use variable
names instead of `$1` and support default values, last time i've tried it did
not work
```sql
CREATE FUNCTION our_add(A BIGINT DEFAULT 3, B BIGINT DEFAULT 1)
RETURNS BIGINT
RETURN $A - $B
```
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