planner, executor: eliminate extra columns introduced by OrderBy upon…

… Union (#8290)

executor/executor_test.go

@@ -1053,6 +1053,15 @@ func (s *testSuite) TestUnion(c *C) {
 	tk.MustExec("insert into t1 value(1,2),(1,1),(2,2),(2,2),(3,2),(3,2)")
 	tk.MustExec("set @@tidb_max_chunk_size=2;")
 	tk.MustQuery("select count(*) from (select a as c, a as d from t1 union all select a, b from t1) t;").Check(testkit.Rows("12"))
+
+	// #issue 8189 and #issue 8199
+	tk.MustExec("drop table if exists t1")
+	tk.MustExec("drop table if exists t2")
+	tk.MustExec("CREATE TABLE t1 (a int not null, b char (10) not null)")
+	tk.MustExec("insert into t1 values(1,'a'),(2,'b'),(3,'c'),(3,'c')")
+	tk.MustExec("CREATE TABLE t2 (a int not null, b char (10) not null)")
+	tk.MustExec("insert into t2 values(1,'a'),(2,'b'),(3,'c'),(3,'c')")
+	tk.MustQuery("select a from t1 union select a from t1 order by (select a+1);").Check(testkit.Rows("1", "2", "3"))
 }
 
 func (s *testSuite) TestNeighbouringProj(c *C) {

plan/logical_plan_builder.go

@@ -713,6 +713,8 @@ func (b *planBuilder) buildUnion(union *ast.UnionStmt) LogicalPlan {
 		unionPlan = unionAllPlan
 	}
 
+	oldLen := unionPlan.Schema().Len()
+
 	if union.OrderBy != nil {
 		unionPlan = b.buildSort(unionPlan, union.OrderBy.Items, nil)
 		if b.err != nil {
@@ -727,6 +729,20 @@ func (b *planBuilder) buildUnion(union *ast.UnionStmt) LogicalPlan {
 			return nil
 		}
 	}
+
+	// Fix issue #8189 (https://github.com/pingcap/tidb/issues/8189).
+	// If there are extra expressions generated from `ORDER BY` clause, generate a `Projection` to remove them.
+	if oldLen != unionPlan.Schema().Len() {
+		proj := LogicalProjection{Exprs: expression.Column2Exprs(unionPlan.Schema().Columns[:oldLen])}.init(b.ctx)
+		proj.SetChildren(unionPlan)
+		schema := expression.NewSchema(unionPlan.Schema().Clone().Columns[:oldLen]...)
+		for _, col := range schema.Columns {
+			col.FromID = proj.ID()
+		}
+		proj.SetSchema(schema)
+		return proj
+	}
+
 	return unionPlan
 }
 
@@ -862,7 +878,7 @@ func (b *planBuilder) buildLimit(src LogicalPlan, limit *ast.Limit) LogicalPlan
 	return li
 }
 
-// colMatch(a,b) means that if a match b, e.g. t.a can match test.t.a but test.t.a can't match t.a.
+// colMatch means that if a match b, e.g. t.a can match test.t.a but test.t.a can't match t.a.
 // Because column a want column from database test exactly.
 func colMatch(a *ast.ColumnName, b *ast.ColumnName) bool {
 	if a.Schema.L == "" || a.Schema.L == b.Schema.L {
@@ -912,7 +928,7 @@ func resolveFromSelectFields(v *ast.ColumnNameExpr, fields []*ast.SelectField, i
 	return
 }
 
-// AggregateFuncExtractor visits Expr tree.
+// havingAndOrderbyExprResolver visits Expr tree.
 // It converts ColunmNameExpr to AggregateFuncExpr and collects AggregateFuncExpr.
 type havingAndOrderbyExprResolver struct {
 	inAggFunc    bool

plan/logical_plan_test.go

@@ -1459,6 +1459,16 @@ func (s *testPlanSuite) TestUnion(c *C) {
 			best: "",
 			err:  true,
 		},
+		{
+			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,
+		},
+		{
+			sql:  "select * from (select 1 as a  union select 1 union all select 2) t order by (select a)",
+			best: "Apply{UnionAll{UnionAll{Dual->Projection->Projection->Dual->Projection->Projection}->Aggr(firstrow(a))->Projection->Dual->Projection->Projection}->Dual->Projection->MaxOneRow}->Sort->Projection",
+			err:  false,
+		},
 	}
 	for i, tt := range tests {
 		comment := Commentf("case:%v sql:%s", i, tt.sql)