address eurekaka's comments

pingcap · Jun 30, 2019 · 3fd835b · 3fd835b
1 parent 9b6893e
commit 3fd835b
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Showing 2 changed files with 17 additions and 13 deletions.
diff --git a/cmd/explaintest/r/explain_easy.result b/cmd/explaintest/r/explain_easy.result
@@ -194,31 +194,31 @@ HashAgg_18	24000.00	root	group by:c1, funcs:firstrow(join_agg_0)
 explain select count(1) from (select count(1) from (select * from t1 where c3 = 100) k) k2;
 id	count	task	operator info
 StreamAgg_13	1.00	root	funcs:count(1)
-└─StreamAgg_28	1.00	root	funcs:count(col_0)
+└─StreamAgg_28	1.00	root	funcs:firstrow(col_0)
   └─TableReader_29	1.00	root	data:StreamAgg_17
-    └─StreamAgg_17	1.00	cop	funcs:count(1)
+    └─StreamAgg_17	1.00	cop	funcs:firstrow(1)
       └─Selection_27	10.00	cop	eq(test.t1.c3, 100)
         └─TableScan_26	10000.00	cop	table:t1, range:[-inf,+inf], keep order:false, stats:pseudo
 explain select 1 from (select count(c2), count(c3) from t1) k;
 id	count	task	operator info
 Projection_5	1.00	root	1
-└─StreamAgg_17	1.00	root	funcs:count(col_0)
+└─StreamAgg_17	1.00	root	funcs:firstrow(col_0)
   └─TableReader_18	1.00	root	data:StreamAgg_9
-    └─StreamAgg_9	1.00	cop	funcs:count(1)
+    └─StreamAgg_9	1.00	cop	funcs:firstrow(1)
       └─TableScan_16	10000.00	cop	table:t1, range:[-inf,+inf], keep order:false, stats:pseudo
 explain select count(1) from (select max(c2), count(c3) as m from t1) k;
 id	count	task	operator info
 StreamAgg_11	1.00	root	funcs:count(1)
-└─StreamAgg_23	1.00	root	funcs:count(col_0)
+└─StreamAgg_23	1.00	root	funcs:firstrow(col_0)
   └─TableReader_24	1.00	root	data:StreamAgg_15
-    └─StreamAgg_15	1.00	cop	funcs:count(1)
+    └─StreamAgg_15	1.00	cop	funcs:firstrow(1)
       └─TableScan_22	10000.00	cop	table:t1, range:[-inf,+inf], keep order:false, stats:pseudo
 explain select count(1) from (select count(c2) from t1 group by c3) k;
 id	count	task	operator info
 StreamAgg_11	1.00	root	funcs:count(1)
-└─HashAgg_23	8000.00	root	group by:col_0, 
+└─HashAgg_23	8000.00	root	group by:col_1, funcs:firstrow(col_0)
   └─TableReader_24	8000.00	root	data:HashAgg_20
-    └─HashAgg_20	8000.00	cop	group by:test.t1.c3, 
+    └─HashAgg_20	8000.00	cop	group by:test.t1.c3, funcs:firstrow(1)
       └─TableScan_15	10000.00	cop	table:t1, range:[-inf,+inf], keep order:false, stats:pseudo
 set @@session.tidb_opt_insubq_to_join_and_agg=0;
 explain select sum(t1.c1 in (select c1 from t2)) from t1;

diff --git a/planner/core/rule_column_pruning.go b/planner/core/rule_column_pruning.go
@@ -119,15 +119,19 @@ func (la *LogicalAggregation) PruneColumns(parentUsedCols []*expression.Column)
 	for _, aggrFunc := range la.AggFuncs {
 		selfUsedCols = expression.ExtractColumnsFromExpressions(selfUsedCols, aggrFunc.Args, nil)
 	}
-	if len(la.GroupByItems) == 0 && len(la.AggFuncs) == 0 {
-		// If all the aggregate functions are pruned and there is no group-by item, we should add
-		// an aggregate function to keep the correctness.
-		one, err := aggregation.NewAggFuncDesc(la.ctx, ast.AggFuncCount, []expression.Expression{expression.One}, false)
+	if len(la.AggFuncs) == 0 {
+		// If all the aggregate functions are pruned, we should add an aggregate function to keep the correctness.
+		one, err := aggregation.NewAggFuncDesc(la.ctx, ast.AggFuncFirstRow, []expression.Expression{expression.One}, false)
 		if err != nil {
 			return err
 		}
 		la.AggFuncs = []*aggregation.AggFuncDesc{one}
-		la.schema.Columns = []*expression.Column{{TblName: model.NewCIStr("dummy_cnt"), RetType: types.NewFieldType(mysql.TypeLonglong)}}
+		col := &expression.Column{
+			ColName:  model.NewCIStr("dummy_agg"),
+			UniqueID: la.ctx.GetSessionVars().AllocPlanColumnID(),
+			RetType:  types.NewFieldType(mysql.TypeLonglong),
+		}
+		la.schema.Columns = []*expression.Column{col}
 	}
 
 	if len(la.GroupByItems) > 0 {