planner: fix union statements order (#8214)

pingcap · Nov 15, 2018 · 97e7f16 · 97e7f16
1 parent ff0c436
commit 97e7f16
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Showing 2 changed files with 9 additions and 3 deletions.
diff --git a/plan/logical_plan_builder.go b/plan/logical_plan_builder.go
@@ -698,7 +698,8 @@ func (b *planBuilder) buildUnion(union *ast.UnionStmt) LogicalPlan {
 	if unionDistinctPlan != nil {
 		unionDistinctPlan = b.buildDistinct(unionDistinctPlan, unionDistinctPlan.Schema().Len())
 		if len(allSelectPlans) > 0 {
-			allSelectPlans = append(allSelectPlans, unionDistinctPlan)
+			// Can't change the statements order in order to get the correct column info.
+			allSelectPlans = append([]LogicalPlan{unionDistinctPlan}, allSelectPlans...)
 		}
 	}
 

diff --git a/plan/logical_plan_test.go b/plan/logical_plan_test.go
@@ -1446,7 +1446,7 @@ func (s *testPlanSuite) TestUnion(c *C) {
 		},
 		{
 			sql:  "select a from t union select a from t union all select a from t",
-			best: "UnionAll{DataScan(t)->Projection->UnionAll{DataScan(t)->Projection->DataScan(t)->Projection}->Aggr(firstrow(t.a))->Projection}",
+			best: "UnionAll{UnionAll{DataScan(t)->Projection->DataScan(t)->Projection}->Aggr(firstrow(t.a))->Projection->DataScan(t)->Projection}",
 			err:  false,
 		},
 		{
@@ -1469,6 +1469,11 @@ func (s *testPlanSuite) TestUnion(c *C) {
 			best: "Apply{UnionAll{UnionAll{Dual->Projection->Projection->Dual->Projection->Projection}->Aggr(firstrow(a))->Projection->Dual->Projection->Projection}->Dual->Projection->MaxOneRow}->Sort->Projection",
 			err:  false,
 		},
+		{
+			sql:  "select * from (select 1 as a  union select 1 union all select 2) t order by a",
+			best: "UnionAll{UnionAll{Dual->Projection->Projection->Dual->Projection->Projection}->Aggr(firstrow(a))->Projection->Dual->Projection->Projection}->Projection->Sort",
+			err:  false,
+		},
 	}
 	for i, tt := range tests {
 		comment := Commentf("case:%v sql:%s", i, tt.sql)
@@ -1484,7 +1489,7 @@ func (s *testPlanSuite) TestUnion(c *C) {
 		plan := builder.build(stmt)
 		if tt.err {
 			c.Assert(builder.err, NotNil)
-			return
+			continue
 		}
 		c.Assert(builder.err, IsNil)
 		p := plan.(LogicalPlan)