fix empty group_by display

Author: zebsme

datafusion/physical-plan/src/aggregates/mod.rs

@@ -836,7 +836,9 @@ impl DisplayAs for AggregateExec {
                     .map(|agg| agg.name().to_string())
                     .collect();
                 writeln!(f, "mode={:?}", self.mode)?;
-                writeln!(f, "group_by={}", g.join(", "))?;
+                if !g.is_empty() {
+                    writeln!(f, "group_by={}", g.join(", "))?;
+                }
                 writeln!(f, "aggr={}", a.join(", "))?;
             }
         }

datafusion/sqllogictest/test_files/explain_tree.slt

@@ -1093,22 +1093,28 @@ physical_plan
 11)└───────────────────────────┘└─────────────┬─────────────┘
 12)-----------------------------┌─────────────┴─────────────┐
 13)-----------------------------│       AggregateExec       │
-14)-----------------------------└─────────────┬─────────────┘
-15)-----------------------------┌─────────────┴─────────────┐
-16)-----------------------------│   CoalescePartitionsExec  │
+14)-----------------------------│    --------------------   │
+15)-----------------------------│   aggr: count(Int64(1))   │
+16)-----------------------------│        mode: Final        │
 17)-----------------------------└─────────────┬─────────────┘
 18)-----------------------------┌─────────────┴─────────────┐
-19)-----------------------------│       AggregateExec       │
+19)-----------------------------│   CoalescePartitionsExec  │
 20)-----------------------------└─────────────┬─────────────┘
 21)-----------------------------┌─────────────┴─────────────┐
-22)-----------------------------│      RepartitionExec      │
-23)-----------------------------└─────────────┬─────────────┘
-24)-----------------------------┌─────────────┴─────────────┐
-25)-----------------------------│       DataSourceExec      │
-26)-----------------------------│    --------------------   │
-27)-----------------------------│          files: 1         │
-28)-----------------------------│      format: parquet      │
-29)-----------------------------└───────────────────────────┘
+22)-----------------------------│       AggregateExec       │
+23)-----------------------------│    --------------------   │
+24)-----------------------------│   aggr: count(Int64(1))   │
+25)-----------------------------│       mode: Partial       │
+26)-----------------------------└─────────────┬─────────────┘
+27)-----------------------------┌─────────────┴─────────────┐
+28)-----------------------------│      RepartitionExec      │
+29)-----------------------------└─────────────┬─────────────┘
+30)-----------------------------┌─────────────┴─────────────┐
+31)-----------------------------│       DataSourceExec      │
+32)-----------------------------│    --------------------   │
+33)-----------------------------│          files: 1         │
+34)-----------------------------│      format: parquet      │
+35)-----------------------------└───────────────────────────┘
 
 # Query with cross join.
 query TT