Support join cardinality estimation if distinct_count is set

Currently we require max and min to be set, as they might be used to
estimate the distinct count. This is unnecessarily conservative if
distinct_count has actually been provided, in which case max and min
won't be used at all and the presence of max or min has no influence
over how good of an estimate it is.

Author: jackkleeman

datafusion/physical-plan/src/joins/utils.rs

@@ -563,11 +563,14 @@ fn estimate_inner_join_cardinality(
         .iter()
         .zip(right_stats.column_statistics.iter())
     {
-        // Break if any of statistics bounds are undefined
-        if left_stat.min_value.get_value().is_none()
-            || left_stat.max_value.get_value().is_none()
-            || right_stat.min_value.get_value().is_none()
-            || right_stat.max_value.get_value().is_none()
+        // Break if we don't have enough information to calculate a distinct count
+        // If distinct_count isn't provided directly, we need min and max to be provided
+        if (left_stat.distinct_count.get_value().is_none()
+            && (left_stat.min_value.get_value().is_none()
+                || left_stat.max_value.get_value().is_none()))
+            || (right_stat.distinct_count.get_value().is_none()
+                && (right_stat.min_value.get_value().is_none()
+                    || right_stat.max_value.get_value().is_none()))
         {
             return None;
         }
@@ -2016,20 +2019,20 @@ mod tests {
             ),
             // When we have distinct count.
             (
-                (10, Inexact(1), Inexact(10), Inexact(10), Absent),
-                (10, Inexact(1), Inexact(10), Inexact(10), Absent),
+                (10, Absent, Absent, Inexact(10), Absent),
+                (10, Absent, Absent, Inexact(10), Absent),
                 Some(Inexact(10)),
             ),
             // distinct(left) > distinct(right)
             (
-                (10, Inexact(1), Inexact(10), Inexact(5), Absent),
-                (10, Inexact(1), Inexact(10), Inexact(2), Absent),
+                (10, Absent, Absent, Inexact(5), Absent),
+                (10, Absent, Absent, Inexact(2), Absent),
                 Some(Inexact(20)),
             ),
             // distinct(right) > distinct(left)
             (
-                (10, Inexact(1), Inexact(10), Inexact(2), Absent),
-                (10, Inexact(1), Inexact(10), Inexact(5), Absent),
+                (10, Absent, Absent, Inexact(2), Absent),
+                (10, Absent, Absent, Inexact(5), Absent),
                 Some(Inexact(20)),
             ),
             // min(left) < 0 (range(left) > range(right))
@@ -2071,18 +2074,13 @@ mod tests {
             ),
             // No min or max (or both).
             (
-                (10, Absent, Absent, Inexact(3), Absent),
-                (10, Absent, Absent, Inexact(3), Absent),
-                None,
-            ),
-            (
-                (10, Inexact(2), Absent, Inexact(3), Absent),
-                (10, Absent, Inexact(5), Inexact(3), Absent),
+                (10, Absent, Absent, Absent, Absent),
+                (10, Absent, Absent, Absent, Absent),
                 None,
             ),
             (
-                (10, Absent, Inexact(3), Inexact(3), Absent),
-                (10, Inexact(1), Absent, Inexact(3), Absent),
+                (10, Inexact(2), Absent, Absent, Absent),
+                (10, Absent, Inexact(5), Absent, Absent),
                 None,
             ),
             (