[branch-50] Extend datatype semantic equality check to include timestamps (#17777) (#18129)

## Which issue does this PR close?

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- Related to #17776
- Related to #18072

## Rationale for this change

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If I've understood semantic equality correctly, any two timestamps
should meet the bar for equality regardless of time units and timezones,
but the current code doesn't reflect that.

## What changes are included in this PR?

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Adds a branch to this method for timestamps.

## Are these changes tested?

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Yes

## Are there any user-facing changes?

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Yes

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---------

Co-authored-by: Shiv Bhatia <shivbhatia10@gmail.com>
Co-authored-by: Shiv Bhatia <sbhatia@palantir.com>
Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: 4 people

datafusion/common/src/dfschema.rs

@@ -747,7 +747,8 @@ impl DFSchema {
     }
 
     /// Returns true of two [`DataType`]s are semantically equal (same
-    /// name and type), ignoring both metadata and nullability, and decimal precision/scale.
+    /// name and type), ignoring both metadata and nullability, decimal precision/scale,
+    /// and timezone time units/timezones.
     ///
     /// request to upstream: <https://github.com/apache/arrow-rs/issues/3199>
     pub fn datatype_is_semantically_equal(dt1: &DataType, dt2: &DataType) -> bool {
@@ -806,6 +807,10 @@ impl DFSchema {
                 DataType::Decimal256(_l_precision, _l_scale),
                 DataType::Decimal256(_r_precision, _r_scale),
             ) => true,
+            (
+                DataType::Timestamp(_l_time_unit, _l_timezone),
+                DataType::Timestamp(_r_time_unit, _r_timezone),
+            ) => true,
             _ => dt1 == dt2,
         }
     }
@@ -1596,6 +1601,14 @@ mod tests {
             &DataType::Int16
         ));
 
+        // Any two timestamp types should match
+        assert!(DFSchema::datatype_is_semantically_equal(
+            &DataType::Timestamp(
+                arrow::datatypes::TimeUnit::Microsecond,
+                Some("UTC".into())
+            ),
+            &DataType::Timestamp(arrow::datatypes::TimeUnit::Millisecond, None),
+        ));
         // Test lists
 
         // Succeeds if both have the same element type, disregards names and nullability