Informative Error Message for LAG and LEAD functions

datafusion/core/src/physical_plan/windows/mod.rs

@@ -72,13 +72,19 @@ pub fn create_window_expr(
 fn get_scalar_value_from_args(
     args: &[Arc<dyn PhysicalExpr>],
     index: usize,
-) -> Option<ScalarValue> {
-    args.get(index).map(|v| {
-        v.as_any()
+) -> Result<Option<ScalarValue>> {
+    Ok(if let Some(field) = args.get(index) {
+        let tmp = field
+            .as_any()
             .downcast_ref::<Literal>()
-            .unwrap()
+            .ok_or_else(|| DataFusionError::NotImplemented(
+                format!("There is only support Literal types for field at idx: {} in Window Function", index),
+            ))?
             .value()
-            .clone()
+            .clone();
+        Some(tmp)
+    } else {
+        None
     })
 }
 
@@ -98,20 +104,20 @@ fn create_built_in_window_expr(
             let coerced_args = coerce(args, input_schema, &signature_for_built_in(fun))?;
             let arg = coerced_args[0].clone();
             let data_type = args[0].data_type(input_schema)?;
-            let shift_offset = get_scalar_value_from_args(&coerced_args, 1)
+            let shift_offset = get_scalar_value_from_args(&coerced_args, 1)?
                 .map(|v| v.try_into())
                 .and_then(|v| v.ok());
-            let default_value = get_scalar_value_from_args(&coerced_args, 2);
+            let default_value = get_scalar_value_from_args(&coerced_args, 2)?;
             Arc::new(lag(name, data_type, arg, shift_offset, default_value))
         }
         BuiltInWindowFunction::Lead => {
             let coerced_args = coerce(args, input_schema, &signature_for_built_in(fun))?;
             let arg = coerced_args[0].clone();
             let data_type = args[0].data_type(input_schema)?;
-            let shift_offset = get_scalar_value_from_args(&coerced_args, 1)
+            let shift_offset = get_scalar_value_from_args(&coerced_args, 1)?
                 .map(|v| v.try_into())
                 .and_then(|v| v.ok());
-            let default_value = get_scalar_value_from_args(&coerced_args, 2);
+            let default_value = get_scalar_value_from_args(&coerced_args, 2)?;
             Arc::new(lead(name, data_type, arg, shift_offset, default_value))
         }
         BuiltInWindowFunction::NthValue => {

datafusion/core/tests/sql/window.rs

@@ -1210,6 +1210,26 @@ async fn window_frame_groups_query() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn window_frame_lag() -> Result<()> {
+    let ctx = SessionContext::new();
+    register_aggregate_csv(&ctx).await?;
+    // execute the query
+    let df = ctx
+        .sql(
+            "SELECT c2,
+                lag(c2, c2, c2) OVER () as lag1
+                FROM aggregate_test_100;",
+        )
+        .await?;
+    let err = df.collect().await.unwrap_err();
+    assert_eq!(
+        err.to_string(),
+        "This feature is not implemented: There is only support Literal types for field at idx: 1 in Window Function".to_owned()
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn window_frame_creation() -> Result<()> {
     let ctx = SessionContext::new();