ScalarUDF with zero arguments should be provided with one null array as parameter

datafusion/core/src/physical_optimizer/projection_pushdown.rs

@@ -1270,6 +1270,7 @@ mod tests {
                 ],
                 DataType::Int32,
                 None,
+                false,
             )),
             Arc::new(CaseExpr::try_new(
                 Some(Arc::new(Column::new("d", 2))),
@@ -1336,6 +1337,7 @@ mod tests {
                 ],
                 DataType::Int32,
                 None,
+                false,
             )),
             Arc::new(CaseExpr::try_new(
                 Some(Arc::new(Column::new("d", 3))),
@@ -1405,6 +1407,7 @@ mod tests {
                 ],
                 DataType::Int32,
                 None,
+                false,
             )),
             Arc::new(CaseExpr::try_new(
                 Some(Arc::new(Column::new("d", 2))),
@@ -1471,6 +1474,7 @@ mod tests {
                 ],
                 DataType::Int32,
                 None,
+                false,
             )),
             Arc::new(CaseExpr::try_new(
                 Some(Arc::new(Column::new("d_new", 3))),

datafusion/core/tests/user_defined/user_defined_scalar_functions.rs

@@ -16,15 +16,19 @@
 // under the License.
 
 use arrow::compute::kernels::numeric::add;
-use arrow_array::{ArrayRef, Float64Array, Int32Array, RecordBatch};
+use arrow_array::{Array, ArrayRef, Float64Array, Int32Array, RecordBatch, UInt8Array};
+use arrow_schema::DataType::Float64;
 use arrow_schema::{DataType, Field, Schema};
 use datafusion::prelude::*;
 use datafusion::{execution::registry::FunctionRegistry, test_util};
 use datafusion_common::cast::as_float64_array;
 use datafusion_common::{assert_batches_eq, cast::as_int32_array, Result, ScalarValue};
 use datafusion_expr::{
-    create_udaf, create_udf, Accumulator, ColumnarValue, LogicalPlanBuilder, Volatility,
+    create_udaf, create_udf, Accumulator, ColumnarValue, LogicalPlanBuilder, ScalarUDF,
+    ScalarUDFImpl, Signature, Volatility,
 };
+use rand::{thread_rng, Rng};
+use std::iter;
 use std::sync::Arc;
 
 /// test that casting happens on udfs.
@@ -166,10 +170,7 @@ async fn scalar_udf_zero_params() -> Result<()> {
 
     ctx.register_batch("t", batch)?;
     // create function just returns 100 regardless of inp
-    let myfunc = Arc::new(|args: &[ColumnarValue]| {
-        let ColumnarValue::Scalar(_) = &args[0] else {
-            panic!("expect scalar")
-        };
+    let myfunc = Arc::new(|_args: &[ColumnarValue]| {
         Ok(ColumnarValue::Array(
             Arc::new((0..1).map(|_| 100).collect::<Int32Array>()) as ArrayRef,
         ))
@@ -392,6 +393,107 @@ async fn test_user_defined_functions_with_alias() -> Result<()> {
     Ok(())
 }
 
+#[derive(Debug)]
+pub struct RandomUDF {
+    signature: Signature,
+}
+
+impl RandomUDF {
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::any(0, Volatility::Volatile),
+        }
+    }
+}
+
+impl ScalarUDFImpl for RandomUDF {
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "random_udf"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
+        Ok(Float64)
+    }
+
+    fn invoke(&self, args: &[ColumnarValue]) -> Result<ColumnarValue> {
+        let len: usize = match &args[0] {
+            // This udf is always invoked with zero argument so its argument
+            // is a null array indicating the batch size.
+            ColumnarValue::Array(array) if array.data_type().is_null() => array.len(),
+            _ => {
+                return Err(datafusion::error::DataFusionError::Internal(
+                    "Invalid argument type".to_string(),
+                ))
+            }
+        };
+        let mut rng = thread_rng();
+        let values = iter::repeat_with(|| rng.gen_range(0.1..1.0)).take(len);
+        let array = Float64Array::from_iter_values(values);
+        Ok(ColumnarValue::Array(Arc::new(array)))
+    }
+}
+
+/// Ensure that a user defined function with zero argument will be invoked
+/// with a null array indicating the batch size.
+#[tokio::test]
+async fn test_user_defined_functions_zero_argument() -> Result<()> {
+    let ctx = SessionContext::new();
+
+    let schema = Arc::new(Schema::new(vec![Field::new(
+        "index",
+        DataType::UInt8,
+        false,
+    )]));
+
+    let batch = RecordBatch::try_new(
+        schema,
+        vec![Arc::new(UInt8Array::from_iter_values([1, 2, 3]))],
+    )?;
+
+    ctx.register_batch("data_table", batch)?;
+
+    let random_normal_udf = ScalarUDF::from(RandomUDF::new());
+    ctx.register_udf(random_normal_udf);
+
+    let result = plan_and_collect(
+        &ctx,
+        "SELECT random_udf() AS random_udf, random() AS native_random FROM data_table",
+    )
+    .await?;
+
+    assert_eq!(result.len(), 1);
+    let batch = &result[0];
+    let random_udf = batch
+        .column(0)
+        .as_any()
+        .downcast_ref::<Float64Array>()
+        .unwrap();
+    let native_random = batch
+        .column(1)
+        .as_any()
+        .downcast_ref::<Float64Array>()
+        .unwrap();
+
+    assert_eq!(random_udf.len(), native_random.len());
+
+    let mut previous = -1.0;
+    for i in 0..random_udf.len() {
+        assert!(random_udf.value(i) >= 0.0 && random_udf.value(i) < 1.0);
+        assert!(random_udf.value(i) != previous);
+        previous = random_udf.value(i);
+    }
+
+    Ok(())
+}
+
 fn create_udf_context() -> SessionContext {
     let ctx = SessionContext::new();
     // register a custom UDF

datafusion/physical-expr/src/functions.rs

@@ -81,6 +81,7 @@ pub fn create_physical_expr(
         input_phy_exprs.to_vec(),
         data_type,
         monotonicity,
+        fun.signature().type_signature.supports_zero_argument(),
     )))
 }
 

datafusion/physical-expr/src/planner.rs

@@ -259,7 +259,7 @@ pub fn create_physical_expr(
         }
 
         Expr::ScalarFunction(ScalarFunction { func_def, args }) => {
-            let mut physical_args = args
+            let physical_args = args
                 .iter()
                 .map(|e| create_physical_expr(e, input_dfschema, execution_props))
                 .collect::<Result<Vec<_>>>()?;
@@ -272,17 +272,11 @@ pub fn create_physical_expr(
                         execution_props,
                     )
                 }
-                ScalarFunctionDefinition::UDF(fun) => {
-                    // udfs with zero params expect null array as input
-                    if args.is_empty() {
-                        physical_args.push(Arc::new(Literal::new(ScalarValue::Null)));
-                    }
-                    udf::create_physical_expr(
-                        fun.clone().as_ref(),
-                        &physical_args,
-                        input_schema,
-                    )
-                }
+                ScalarFunctionDefinition::UDF(fun) => udf::create_physical_expr(
+                    fun.clone().as_ref(),
+                    &physical_args,
+                    input_schema,
+                ),
                 ScalarFunctionDefinition::Name(_) => {
                     internal_err!("Function `Expr` with name should be resolved.")
                 }

datafusion/physical-expr/src/scalar_function.rs

@@ -58,6 +58,8 @@ pub struct ScalarFunctionExpr {
     // and it specifies the effect of an increase or decrease in
     // the corresponding `arg` to the function value.
     monotonicity: Option<FuncMonotonicity>,
+    // Whether this function can be invoked with zero arguments
+    supports_zero_argument: bool,
 }
 
 impl Debug for ScalarFunctionExpr {
@@ -79,13 +81,15 @@ impl ScalarFunctionExpr {
         args: Vec<Arc<dyn PhysicalExpr>>,
         return_type: DataType,
         monotonicity: Option<FuncMonotonicity>,
+        supports_zero_argument: bool,
     ) -> Self {
         Self {
             fun,
             name: name.to_owned(),
             args,
             return_type,
             monotonicity,
+            supports_zero_argument,
         }
     }
 
@@ -138,9 +142,12 @@ impl PhysicalExpr for ScalarFunctionExpr {
     fn evaluate(&self, batch: &RecordBatch) -> Result<ColumnarValue> {
         // evaluate the arguments, if there are no arguments we'll instead pass in a null array
         // indicating the batch size (as a convention)
-        let inputs = match (self.args.len(), self.name.parse::<BuiltinScalarFunction>()) {
+        let inputs = match (
+            self.args.is_empty(),
+            self.name.parse::<BuiltinScalarFunction>(),
+        ) {
             // MakeArray support zero argument but has the different behavior from the array with one null.
-            (0, Ok(scalar_fun))
+            (true, Ok(scalar_fun))
                 if scalar_fun
                     .signature()
                     .type_signature
@@ -149,6 +156,11 @@ impl PhysicalExpr for ScalarFunctionExpr {
             {
                 vec![ColumnarValue::create_null_array(batch.num_rows())]
             }
+            // If the function supports zero argument, we pass in a null array indicating the batch size.
+            // This is for user-defined functions.
+            (true, Err(_)) if self.supports_zero_argument => {
+                vec![ColumnarValue::create_null_array(batch.num_rows())]
+            }
             _ => self
                 .args
                 .iter()
@@ -175,6 +187,7 @@ impl PhysicalExpr for ScalarFunctionExpr {
             children,
             self.return_type().clone(),
             self.monotonicity.clone(),
+            self.supports_zero_argument,
         )))
     }
 

datafusion/physical-expr/src/udf.rs

@@ -40,6 +40,7 @@ pub fn create_physical_expr(
         input_phy_exprs.to_vec(),
         fun.return_type(&input_exprs_types)?,
         fun.monotonicity()?,
+        fun.signature().type_signature.supports_zero_argument(),
     )))
 }
 

datafusion/proto/src/physical_plan/from_proto.rs

@@ -340,21 +340,17 @@ pub fn parse_physical_expr(
             // TODO Do not create new the ExecutionProps
             let execution_props = ExecutionProps::new();
 
-            let fun_expr = functions::create_physical_fun(
+            functions::create_physical_expr(
                 &(&scalar_function).into(),
+                &args,
+                input_schema,
                 &execution_props,
-            )?;
-
-            Arc::new(ScalarFunctionExpr::new(
-                &e.name,
-                fun_expr,
-                args,
-                convert_required!(e.return_type)?,
-                None,
-            ))
+            )?
         }
         ExprType::ScalarUdf(e) => {
-            let scalar_fun = registry.udf(e.name.as_str())?.fun().clone();
+            let udf = registry.udf(e.name.as_str())?;
+            let signature = udf.signature();
+            let scalar_fun = udf.fun().clone();
 
             let args = e
                 .args
@@ -368,6 +364,7 @@ pub fn parse_physical_expr(
                 args,
                 convert_required!(e.return_type)?,
                 None,
+                signature.type_signature.supports_zero_argument(),
             ))
         }
         ExprType::LikeExpr(like_expr) => Arc::new(LikeExpr::new(

datafusion/proto/tests/cases/roundtrip_physical_plan.rs

@@ -578,8 +578,9 @@ fn roundtrip_builtin_scalar_function() -> Result<()> {
         "acos",
         fun_expr,
         vec![col("a", &schema)?],
-        DataType::Int64,
+        DataType::Float64,
         None,
+        false,
     );
 
     let project =
@@ -617,6 +618,7 @@ fn roundtrip_scalar_udf() -> Result<()> {
         vec![col("a", &schema)?],
         DataType::Int64,
         None,
+        false,
     );
 
     let project =