planner: regard NULL as point when accessing composite index

distsql/request_builder.go

@@ -721,6 +721,8 @@ func encodeIndexKey(sc *stmtctx.StatementContext, ran *ranger.Range) ([]byte, []
 		}
 	}
 
+	// NOTE: this is a hard-code operation to avoid wrong results when accessing unique index with NULL;
+	// Please see https://github.com/pingcap/tidb/issues/29650 for more details
 	if hasNull {
 		// Append 0 to make unique-key range [null, null] to be a scan rather than point-get.
 		high = kv.Key(high).Next()

planner/core/common_plans.go

@@ -1501,7 +1501,7 @@ func IsPointGetWithPKOrUniqueKeyByAutoCommit(ctx sessionctx.Context, p Plan) (bo
 		return indexScan.IsPointGetByUniqueKey(ctx), nil
 	case *PhysicalTableReader:
 		tableScan := v.TablePlans[0].(*PhysicalTableScan)
-		isPointRange := len(tableScan.Ranges) == 1 && tableScan.Ranges[0].IsPoint(ctx)
+		isPointRange := len(tableScan.Ranges) == 1 && tableScan.Ranges[0].IsPointNonNullable(ctx)
 		if !isPointRange {
 			return false, nil
 		}

planner/core/find_best_task.go

@@ -843,7 +843,8 @@ func (ds *DataSource) findBestTask(prop *property.PhysicalProperty, planCounter
 		if canConvertPointGet {
 			allRangeIsPoint := true
 			for _, ran := range path.Ranges {
-				if !ran.IsPoint(ds.ctx) {
+				if !ran.IsPointNonNullable(ds.ctx) {
+					// unique indexes can have duplicated NULL rows so we cannot use PointGet if there is NULL
 					allRangeIsPoint = false
 					break
 				}

planner/core/integration_test.go

@@ -4835,6 +4835,56 @@ func (s *testIntegrationSerialSuite) TestRejectSortForMPP(c *C) {
 	}
 }
 
+func (s *testIntegrationSerialSuite) TestRegardNULLAsPoint(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+
+	tk.MustExec("drop table if exists tpk")
+	tk.MustExec(`create table tuk (a int, b int, c int, unique key (a, b, c))`)
+	tk.MustExec(`create table tik (a int, b int, c int, key (a, b, c))`)
+	for _, va := range []string{"NULL", "1"} {
+		for _, vb := range []string{"NULL", "1"} {
+			for _, vc := range []string{"NULL", "1"} {
+				tk.MustExec(fmt.Sprintf(`insert into tuk values (%v, %v, %v)`, va, vb, vc))
+				tk.MustExec(fmt.Sprintf(`insert into tik values (%v, %v, %v)`, va, vb, vc))
+				if va == "1" && vb == "1" && vc == "1" {
+					continue
+				}
+				// duplicated NULL rows
+				tk.MustExec(fmt.Sprintf(`insert into tuk values (%v, %v, %v)`, va, vb, vc))
+				tk.MustExec(fmt.Sprintf(`insert into tik values (%v, %v, %v)`, va, vb, vc))
+			}
+		}
+	}
+
+	var input []string
+	var output []struct {
+		SQL          string
+		PlanEnabled  []string
+		PlanDisabled []string
+		Result       []string
+	}
+	s.testData.GetTestCases(c, &input, &output)
+	for i, tt := range input {
+		s.testData.OnRecord(func() {
+			output[i].SQL = tt
+			tk.MustExec(`set @@session.tidb_regard_null_as_point=true`)
+			output[i].PlanEnabled = s.testData.ConvertRowsToStrings(tk.MustQuery("explain " + tt).Rows())
+			output[i].Result = s.testData.ConvertRowsToStrings(tk.MustQuery(tt).Rows())
+
+			tk.MustExec(`set @@session.tidb_regard_null_as_point=false`)
+			output[i].PlanDisabled = s.testData.ConvertRowsToStrings(tk.MustQuery("explain " + tt).Rows())
+		})
+		tk.MustExec(`set @@session.tidb_regard_null_as_point=true`)
+		tk.MustQuery("explain " + tt).Check(testkit.Rows(output[i].PlanEnabled...))
+		tk.MustQuery(tt).Check(testkit.Rows(output[i].Result...))
+
+		tk.MustExec(`set @@session.tidb_regard_null_as_point=false`)
+		tk.MustQuery("explain " + tt).Check(testkit.Rows(output[i].PlanDisabled...))
+		tk.MustQuery(tt).Check(testkit.Rows(output[i].Result...))
+	}
+}
+
 func (s *testIntegrationSuite) TestIssues29711(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")

planner/core/partition_pruner_test.go

@@ -93,6 +93,7 @@ func (s *testPartitionPruneSuit) TestListPartitionPruner(c *C) {
 	tk.MustExec("use test_partition")
 	tk.Se.GetSessionVars().EnableClusteredIndex = variable.ClusteredIndexDefModeIntOnly
 	tk.MustExec("set @@session.tidb_enable_list_partition = ON")
+	tk.MustExec(`set @@session.tidb_regard_null_as_point=false`)
 	tk.MustExec("create table t1 (id int, a int, b int                 ) partition by list (    a    ) (partition p0 values in (1,2,3,4,5), partition p1 values in (6,7,8,9,10,null));")
 	tk.MustExec("create table t2 (a int, id int, b int) partition by list (a*3 + b - 2*a - b) (partition p0 values in (1,2,3,4,5), partition p1 values in (6,7,8,9,10,null));")
 	tk.MustExec("create table t3 (b int, id int, a int) partition by list columns (a) (partition p0 values in (1,2,3,4,5), partition p1 values in (6,7,8,9,10,null));")
@@ -169,6 +170,7 @@ func (s *testPartitionPruneSuit) TestListColumnsPartitionPruner(c *C) {
 	// tk1 use to test partition table with index.
 	tk1 := testkit.NewTestKit(c, s.store)
 	tk1.MustExec("drop database if exists test_partition_1;")
+	tk1.MustExec(`set @@session.tidb_regard_null_as_point=false`)
 	tk1.MustExec("create database test_partition_1")
 	tk1.MustExec("use test_partition_1")
 	tk1.MustExec("set @@session.tidb_enable_list_partition = ON")
@@ -180,6 +182,7 @@ func (s *testPartitionPruneSuit) TestListColumnsPartitionPruner(c *C) {
 	// tk2 use to compare the result with normal table.
 	tk2 := testkit.NewTestKit(c, s.store)
 	tk2.MustExec("drop database if exists test_partition_2;")
+	tk2.MustExec(`set @@session.tidb_regard_null_as_point=false`)
 	tk2.MustExec("create database test_partition_2")
 	tk2.MustExec("use test_partition_2")
 	tk2.MustExec("create table t1 (id int, a int, b int)")

planner/core/physical_plans.go

@@ -1201,7 +1201,7 @@ func (p *PhysicalIndexScan) IsPointGetByUniqueKey(sctx sessionctx.Context) bool
 	return len(p.Ranges) == 1 &&
 		p.Index.Unique &&
 		len(p.Ranges[0].LowVal) == len(p.Index.Columns) &&
-		p.Ranges[0].IsPoint(sctx)
+		p.Ranges[0].IsPointNonNullable(sctx)
 }
 
 // PhysicalSelection represents a filter.

planner/core/plan_to_pb.go

@@ -212,6 +212,18 @@ func checkCoverIndex(idx *model.IndexInfo, ranges []*ranger.Range) bool {
 		if len(rg.LowVal) != len(idx.Columns) {
 			return false
 		}
+		for _, v := range rg.LowVal {
+			if v.IsNull() {
+				// a unique index may have duplicated rows with NULLs, so we cannot set the unique attribute to true when the range has NULL
+				// please see https://github.com/pingcap/tidb/issues/29650 for more details
+				return false
+			}
+		}
+		for _, v := range rg.HighVal {
+			if v.IsNull() {
+				return false
+			}
+		}
 	}
 	return true
 }

planner/core/testdata/integration_serial_suite_in.json

@@ -29,6 +29,25 @@
     ]
 
   },
+  {
+    "name": "TestRegardNULLAsPoint",
+    "cases": [
+      "select * from tuk where a<=>null and b=1",
+      "select * from tik where a<=>null and b=1",
+      "select * from tuk where a<=>null and b>0 and b<2",
+      "select * from tik where a<=>null and b>0 and b<2",
+      "select * from tuk where a<=>null and b>=1 and b<2",
+      "select * from tik where a<=>null and b>=1 and b<2",
+      "select * from tuk where a<=>null and b=1 and c=1",
+      "select * from tik where a<=>null and b=1 and c=1",
+      "select * from tuk where a=1 and b<=>null and c=1",
+      "select * from tik where a=1 and b<=>null and c=1",
+      "select * from tuk where a<=>null and b<=>null and c=1",
+      "select * from tik where a<=>null and b<=>null and c=1",
+      "select * from tuk where a<=>null and b<=>null and c<=>null",
+      "select * from tik where a<=>null and b<=>null and c<=>null"
+    ]
+  },
   {
     "name": "TestPushDownToTiFlashWithKeepOrder",
     "cases": [