Don't calculate sum/avg for key columns

Author: erezsh

data_diff/joindiff_tables.py

@@ -235,6 +235,11 @@ def _collect_stats(self, i, table_seg: TableSegment):
 
         # Metrics
         col_exprs = merge_dicts(
+            {
+                f"min_{c}": min_(this[c]),
+                f"max_{c}": max_(this[c]),
+            }
+            if c in table_seg.key_columns else
             {
                 f"sum_{c}": sum_(this[c]),
                 f"avg_{c}": avg(this[c]),