[GitHub] [arrow-datafusion] Ted-Jiang commented on a diff in pull request #2177: User Defined Table Function (udtf) support

[GitBox <gi...@apache.org>]

Ted-Jiang commented on code in PR #2177:
URL: https://github.com/apache/arrow-datafusion/pull/2177#discussion_r860542317


##########
datafusion/expr/src/function.rs:
##########
@@ -39,6 +40,10 @@ use std::sync::Arc;
 pub type ScalarFunctionImplementation =
     Arc<dyn Fn(&[ColumnarValue]) -> Result<ColumnarValue> + Send + Sync>;
 
+/// Table function. Second tuple
+pub type TableFunctionImplementation =
+    Arc<dyn Fn(&[ColumnarValue], usize) -> Result<(ArrayRef, Vec<usize>)> + Send + Sync>;

Review Comment:
   as  ArrayRef is one of ColumnarValue
   ``` Rust
   pub enum ColumnarValue {
       /// Array of values
       Array(ArrayRef),
       /// A single value
       Scalar(ScalarValue),
   }
   ```
   I think `TableFunctionImplementation ` is same as `ScalarFunctionImplementation `.
   And it only generate table N*1 , if we use as https://github.com/apache/arrow-datafusion/pull/2177#issuecomment-1100368801
   ```rust
   Arc<dyn Fn(&[ColumnarValue], usize) -> Result<(Vec< ColumnarValue >, Vec<usize>)> + Send + Sync>;
   ```
   We could generate N*M table
   If im wrong plz correct me? 



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