fix: Remove !=0 check from supports_collect_by_thresholds (#20730)

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## Rationale for this change
Small change to remove the TODO + != 0 check. Since the commit was made
two years ago, statistics have been changed to use Precision. Exact(0)
and inexact(0) are now valid stats while absent will evaluate to false
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---------

Co-authored-by: Daniël Heres <danielheres@gmail.com>

Author: jonathanc-n

datafusion/physical-optimizer/src/join_selection.rs

@@ -87,16 +87,18 @@ fn supports_collect_by_thresholds(
     threshold_byte_size: usize,
     threshold_num_rows: usize,
 ) -> bool {
-    // Currently we do not trust the 0 value from stats, due to stats collection might have bug
-    // TODO check the logic in datasource::get_statistics_with_limit()
     let Ok(stats) = plan.partition_statistics(None) else {
         return false;
     };
 
+    // Stats use `Precision<T>` to represent stats, where `Absent` means unknown.
+    // `Exact(0)` and `Inexact(0)` are both valid stats, and we should not treat
+    // them as unknown, `Absent` will return None (this is in regards to why
+    // `!=0` is not checked)
     if let Some(byte_size) = stats.total_byte_size.get_value() {
-        *byte_size != 0 && *byte_size < threshold_byte_size
+        *byte_size < threshold_byte_size
     } else if let Some(num_rows) = stats.num_rows.get_value() {
-        *num_rows != 0 && *num_rows < threshold_num_rows
+        *num_rows < threshold_num_rows
     } else {
         false
     }

datafusion/sqllogictest/test_files/cte.slt

@@ -1015,7 +1015,7 @@ logical_plan
 04)----SubqueryAlias: cte
 05)------TableScan: person projection=[id]
 physical_plan
-01)HashJoinExec: mode=Partitioned, join_type=LeftSemi, on=[(id@0, id@0)]
+01)HashJoinExec: mode=CollectLeft, join_type=LeftSemi, on=[(id@0, id@0)]
 02)--DataSourceExec: partitions=1, partition_sizes=[0]
 03)--DataSourceExec: partitions=1, partition_sizes=[0]