fix primary key's type (pingcap#2222)

* executor: fix primay key type error

When we do single read index scan, primay key's type should be determined
by it's flag.

* executor: add test

* executor: format code:

* executor: address comment

executor/executor_distsql.go

@@ -440,8 +440,12 @@ func (e *XSelectIndexExec) nextForSingleRead() (*Row, error) {
 func (e *XSelectIndexExec) indexRowToTableRow(handle int64, indexRow []types.Datum) []types.Datum {
 	tableRow := make([]types.Datum, len(e.indexPlan.Columns))
 	for i, tblCol := range e.indexPlan.Columns {
-		if mysql.HasPriKeyFlag(tblCol.Flag) && e.indexPlan.Table.PKIsHandle {
-			tableRow[i] = types.NewIntDatum(handle)
+		if table.ToColumn(tblCol).IsPKHandleColumn(e.indexPlan.Table) {
+			if mysql.HasUnsignedFlag(tblCol.FieldType.Flag) {
+				tableRow[i] = types.NewUintDatum(uint64(handle))
+			} else {
+				tableRow[i] = types.NewIntDatum(handle)
+			}
 			continue
 		}
 		for j, idxCol := range e.indexPlan.Index.Columns {

executor/executor_test.go

@@ -521,6 +521,14 @@ func (s *testSuite) TestUnion(c *C) {
 	r.Check(testkit.Rows("1"))
 	r = tk.MustQuery("select (select * from t1 where a != t.a union all (select * from t2 where a != t.a) order by a limit 1) from t1 t")
 	r.Check(testkit.Rows("1", "2"))
+
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t (id int unsigned primary key auto_increment, c1 int, c2 int, index c1_c2 (c1, c2))")
+	tk.MustExec("insert into t (c1, c2) values (1, 1)")
+	tk.MustExec("insert into t (c1, c2) values (1, 2)")
+	tk.MustExec("insert into t (c1, c2) values (2, 3)")
+	r = tk.MustQuery("select * from t where t.c1 = 1 union select * from t where t.id = 1")
+	r.Check(testkit.Rows("1 1 1", "2 1 2"))
 }
 
 func (s *testSuite) TestIn(c *C) {