[fix] Add type coercion from NULL to Interval to make date_bin more postgres compatible (#20499)

## Which issue does this PR close?

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- Closes https://github.com/apache/datafusion/issues/20502

## Rationale for this change

The following query is failing with the following error:

`SELECT date_bin(NULL, TIMESTAMP '2023-01-01 12:30:00', TIMESTAMP
'2023-01-01 12:00:00')
`

`Error: Error during planning: Failed to coerce arguments to satisfy a
call to 'date_bin' function: coercion from Null, Timestamp(ns),
Timestamp(ns) to the signature OneOf([....])`

## What changes are included in this PR?

Fix `date_bin(NULL, ...)` to return `NULL` instead of a planning error
by allowing Nulls to coerce to Interva.

## Are these changes tested?

I added a sqllogictest case to verify the query executes and returns
`NULL`.

## Are there any user-facing changes?

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Yes, previously `date_bin(NULL, ...) `returned a planning error. It now
returns NULL.

datafusion/expr/src/type_coercion/functions.rs

@@ -883,7 +883,7 @@ fn coerced_from<'a>(
             Timestamp(TimeUnit::Nanosecond, None),
             Null | Timestamp(_, None) | Date32 | Utf8 | LargeUtf8,
         ) => Some(type_into.clone()),
-        (Interval(_), Utf8 | LargeUtf8) => Some(type_into.clone()),
+        (Interval(_), Null | Utf8 | LargeUtf8) => Some(type_into.clone()),
         // We can go into a Utf8View from a Utf8 or LargeUtf8
         (Utf8View, Utf8 | LargeUtf8 | Null) => Some(type_into.clone()),
         // Any type can be coerced into strings

datafusion/functions/src/datetime/date_bin.rs

@@ -421,6 +421,12 @@ fn date_bin_impl(
     origin: &ColumnarValue,
 ) -> Result<ColumnarValue> {
     let stride = match stride {
+        ColumnarValue::Scalar(s) if s.is_null() => {
+            // NULL stride -> NULL result (standard SQL NULL propagation)
+            return Ok(ColumnarValue::Scalar(ScalarValue::try_from(
+                array.data_type(),
+            )?));
+        }
         ColumnarValue::Scalar(ScalarValue::IntervalDayTime(Some(v))) => {
             let (days, ms) = IntervalDayTimeType::to_parts(*v);
             let nanos = (TimeDelta::try_days(days as i64).unwrap()

datafusion/sqllogictest/test_files/datetime/timestamps.slt

@@ -771,6 +771,18 @@ select to_timestamp_seconds(cast (1 as int));
 ## test date_bin function
 ##########
 
+# NULL stride should return NULL, not a planning error
+query P
+SELECT date_bin(NULL, TIMESTAMP '2023-01-01 12:30:00', TIMESTAMP '2023-01-01 12:00:00')
+----
+NULL
+
+# NULL stride should return NULL, not a planning error
+query P
+SELECT date_bin(NULL, TIMESTAMP '2023-01-01 12:30:00')
+----
+NULL
+
 # invalid second arg type
 query error
 SELECT DATE_BIN(INTERVAL '0 second', 25, TIMESTAMP '1970-01-01T00:00:00Z')