plan: statsInfo.count for LogicalTableDual should be its RowCount (pi…

…ngcap#6190)

plan/cbo_test.go

@@ -123,6 +123,35 @@ func (s *testAnalyzeSuite) TestStraightJoin(c *C) {
 	))
 }
 
+func (s *testAnalyzeSuite) TestTableDual(c *C) {
+	defer testleak.AfterTest(c)()
+	store, dom, err := newStoreWithBootstrap()
+	c.Assert(err, IsNil)
+	defer func() {
+		dom.Close()
+		store.Close()
+	}()
+
+	testKit := testkit.NewTestKit(c, store)
+	testKit.MustExec(`use test`)
+	h := dom.StatsHandle()
+	testKit.MustExec(`create table t(a int)`)
+	testKit.MustExec("insert into t values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10)")
+	c.Assert(h.HandleDDLEvent(<-h.DDLEventCh()), IsNil)
+
+	h.DumpStatsDeltaToKV()
+	c.Assert(h.Update(dom.InfoSchema()), IsNil)
+
+	testKit.MustQuery(`explain select * from t where 1 = 0`).Check(testkit.Rows(
+		`TableDual_6 Projection_5  root rows:0 0.00`,
+		`Projection_5  TableDual_6 root test.t.a 0.00`,
+	))
+
+	testKit.MustQuery(`explain select * from t where 1 = 1 limit 0`).Check(testkit.Rows(
+		`TableDual_5   root rows:0 0.00`,
+	))
+}
+
 func (s *testAnalyzeSuite) TestEstimation(c *C) {
 	defer testleak.AfterTest(c)()
 	store, dom, err := newStoreWithBootstrap()

plan/stats.go

@@ -62,6 +62,18 @@ func (p *basePhysicalPlan) StatsInfo() *statsInfo {
 	return p.stats
 }
 
+func (p *LogicalTableDual) deriveStats() *statsInfo {
+	profile := &statsInfo{
+		count:       float64(p.RowCount),
+		cardinality: make([]float64, p.Schema().Len()),
+	}
+	for i := range profile.cardinality {
+		profile.cardinality[i] = float64(p.RowCount)
+	}
+	p.stats = profile
+	return p.stats
+}
+
 func (p *baseLogicalPlan) deriveStats() *statsInfo {
 	if len(p.children) == 0 {
 		profile := &statsInfo{