Fix: to_char Function Now Correctly Handles DATE Values in DataFusion (#14970)

* revert _to_char_scalar to before #14908

* Amend formatted loop - handle null

* revert _to_char_array to before #14908

* add slt test

Author: kosiew

datafusion/functions/src/datetime/to_char.rs

@@ -212,14 +212,6 @@ fn _to_char_scalar(
     let is_scalar_expression = matches!(&expression, ColumnarValue::Scalar(_));
     let array = expression.into_array(1)?;
 
-    // fix https://github.com/apache/datafusion/issues/14884
-    // If the input date/time is null, return a null Utf8 result.
-    if array.is_null(0) {
-        return Ok(match is_scalar_expression {
-            true => ColumnarValue::Scalar(ScalarValue::Utf8(None)),
-            false => ColumnarValue::Array(new_null_array(&Utf8, array.len())),
-        });
-    }
     if format.is_none() {
         if is_scalar_expression {
             return Ok(ColumnarValue::Scalar(ScalarValue::Utf8(None)));
@@ -234,15 +226,21 @@ fn _to_char_scalar(
     };
 
     let formatter = ArrayFormatter::try_new(array.as_ref(), &format_options)?;
-    let formatted: Result<Vec<_>, ArrowError> = (0..array.len())
-        .map(|i| formatter.value(i).try_to_string())
+    let formatted: Result<Vec<Option<String>>, ArrowError> = (0..array.len())
+        .map(|i| {
+            if array.is_null(i) {
+                Ok(None)
+            } else {
+                formatter.value(i).try_to_string().map(Some)
+            }
+        })
         .collect();
 
     if let Ok(formatted) = formatted {
         if is_scalar_expression {
-            Ok(ColumnarValue::Scalar(ScalarValue::Utf8(Some(
-                formatted.first().unwrap().to_string(),
-            ))))
+            Ok(ColumnarValue::Scalar(ScalarValue::Utf8(
+                formatted.first().unwrap().clone(),
+            )))
         } else {
             Ok(ColumnarValue::Array(
                 Arc::new(StringArray::from(formatted)) as ArrayRef
@@ -260,13 +258,6 @@ fn _to_char_array(args: &[ColumnarValue]) -> Result<ColumnarValue> {
     let data_type = arrays[0].data_type();
 
     for idx in 0..arrays[0].len() {
-        // fix https://github.com/apache/datafusion/issues/14884
-        // If the date/time value is null, push None.
-        if arrays[0].is_null(idx) {
-            results.push(None);
-            continue;
-        }
-
         let format = if format_array.is_null(idx) {
             None
         } else {
@@ -678,31 +669,4 @@ mod tests {
             "Execution error: Format for `to_char` must be non-null Utf8, received Timestamp(Nanosecond, None)"
         );
     }
-
-    #[test]
-    fn test_to_char_input_none_array() {
-        let date_array = Arc::new(Date32Array::from(vec![Some(18506), None])) as ArrayRef;
-        let format_array =
-            StringArray::from(vec!["%Y-%m-%d".to_string(), "%Y-%m-%d".to_string()]);
-        let args = datafusion_expr::ScalarFunctionArgs {
-            args: vec![
-                ColumnarValue::Array(date_array),
-                ColumnarValue::Array(Arc::new(format_array) as ArrayRef),
-            ],
-            number_rows: 2,
-            return_type: &DataType::Utf8,
-        };
-        let result = ToCharFunc::new()
-            .invoke_with_args(args)
-            .expect("Expected no error");
-        if let ColumnarValue::Array(result) = result {
-            let result = result.as_any().downcast_ref::<StringArray>().unwrap();
-            assert_eq!(result.len(), 2);
-            // The first element is valid, second is null.
-            assert!(!result.is_null(0));
-            assert!(result.is_null(1));
-        } else {
-            panic!("Expected an array value");
-        }
-    }
 }

datafusion/sqllogictest/test_files/timestamps.slt

@@ -2847,6 +2847,26 @@ SELECT to_char(null, '%d-%m-%Y');
 ----
 NULL
 
+query T
+SELECT to_char(date_column, '%Y-%m-%d')
+FROM (VALUES 
+    (DATE '2020-09-01'),
+    (NULL)
+) AS t(date_column);
+----
+2020-09-01
+NULL
+
+query T
+SELECT to_char(date_column, '%Y-%m-%d')
+FROM (VALUES 
+    (NULL),
+    (DATE '2020-09-01')
+) AS t(date_column);
+----
+NULL
+2020-09-01
+
 query T
 SELECT to_char(column1, column2)
 FROM