Minor: return "not supported" for COUNT DISTINCT with multiple arguments (#11391)

* Minor: return "not supported" for COUNT DISTINCT with multiple arguments

* update condition

Author: jonahgao

datafusion/functions-aggregate/src/count.rs

@@ -37,7 +37,7 @@ use arrow::{
     buffer::BooleanBuffer,
 };
 use datafusion_common::{
-    downcast_value, internal_err, DataFusionError, Result, ScalarValue,
+    downcast_value, internal_err, not_impl_err, DataFusionError, Result, ScalarValue,
 };
 use datafusion_expr::function::StateFieldsArgs;
 use datafusion_expr::{
@@ -138,6 +138,10 @@ impl AggregateUDFImpl for Count {
             return Ok(Box::new(CountAccumulator::new()));
         }
 
+        if acc_args.input_exprs.len() > 1 {
+            return not_impl_err!("COUNT DISTINCT with multiple arguments");
+        }
+
         let data_type = acc_args.input_type;
         Ok(match data_type {
             // try and use a specialized accumulator if possible, otherwise fall back to generic accumulator

datafusion/sqllogictest/test_files/aggregate.slt

@@ -2019,6 +2019,10 @@ SELECT count(c1, c2) FROM test
 ----
 3
 
+# count(distinct) with multiple arguments
+query error DataFusion error: This feature is not implemented: COUNT DISTINCT with multiple arguments
+SELECT count(distinct c1, c2) FROM test
+
 # count_null
 query III
 SELECT count(null), count(null, null), count(distinct null) FROM test