planner: fix hash partition prune with is null condition

pkg/planner/core/casetest/partition/partition_pruner_test.go

@@ -49,6 +49,7 @@ func TestHashPartitionPruner(t *testing.T) {
 	tk.MustExec("create table t8(a int, b int) partition by hash(a) partitions 6;")
 	tk.MustExec("create table t9(a bit(1) default null, b int(11) default null) partition by hash(a) partitions 3;") //issue #22619
 	tk.MustExec("create table t10(a bigint unsigned) partition BY hash (a);")
+	tk.MustExec("create table t11(a int, b int) partition by hash(a + a + a + b) partitions 5")
 
 	var input []string
 	var output []struct {

pkg/planner/core/casetest/partition/testdata/partition_pruner_in.json

@@ -30,7 +30,10 @@
       "explain format = 'brief' select * from t8 where (a <= 10 and a >= 8) or (a <= 13 and a >= 11) or (a <= 16 and a >= 14)",
       "explain format = 'brief' select * from t8 where a < 12 and a > 9",
       "explain format = 'brief' select * from t9",
-      "explain format = 'brief' select * from t10 where a between 0 AND 15218001646226433652"
+      "explain format = 'brief' select * from t10 where a between 0 AND 15218001646226433652",
+      "explain format = 'brief' select * from t11 where a is null",
+      "explain format = 'brief' select * from t11 where a is null and b = 2",
+      "explain format = 'brief' select * from t11 where a = 1 and b = 2"
     ]
   },
   {

pkg/planner/core/casetest/partition/testdata/partition_pruner_out.json

@@ -215,6 +215,30 @@
           "└─Selection 250.00 cop[tikv]  ge(test_partition.t10.a, 0), le(test_partition.t10.a, 15218001646226433652)",
           "  └─TableFullScan 10000.00 cop[tikv] table:t10 keep order:false, stats:pseudo"
         ]
+      },
+      {
+        "SQL": "explain format = 'brief' select * from t11 where a is null",
+        "Result": [
+          "TableReader 10.00 root partition:all data:Selection",
+          "└─Selection 10.00 cop[tikv]  isnull(test_partition.t11.a)",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t11 keep order:false, stats:pseudo"
+        ]
+      },
+      {
+        "SQL": "explain format = 'brief' select * from t11 where a is null and b = 2",
+        "Result": [
+          "TableReader 0.01 root partition:p0 data:Selection",
+          "└─Selection 0.01 cop[tikv]  eq(test_partition.t11.b, 2), isnull(test_partition.t11.a)",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t11 keep order:false, stats:pseudo"
+        ]
+      },
+      {
+        "SQL": "explain format = 'brief' select * from t11 where a = 1 and b = 2",
+        "Result": [
+          "TableReader 0.01 root partition:p0 data:Selection",
+          "└─Selection 0.01 cop[tikv]  eq(test_partition.t11.a, 1), eq(test_partition.t11.b, 2)",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t11 keep order:false, stats:pseudo"
+        ]
       }
     ]
   },

pkg/planner/core/rule_partition_processor.go

@@ -148,11 +148,18 @@ func generateHashPartitionExpr(ctx base.PlanContext, pi *model.PartitionInfo, co
 func getPartColumnsForHashPartition(hashExpr expression.Expression) ([]*expression.Column, []int) {
 	partCols := expression.ExtractColumns(hashExpr)
 	colLen := make([]int, 0, len(partCols))
+	retCols := make([]*expression.Column, 0, len(partCols))
+	filled := make(map[int64]struct{})
 	for i := 0; i < len(partCols); i++ {
-		partCols[i].Index = i
-		colLen = append(colLen, types.UnspecifiedLength)
+		// Deal with same columns.
+		if _, done := filled[partCols[i].UniqueID]; !done {
+			partCols[i].Index = len(filled)
+			filled[partCols[i].UniqueID] = struct{}{}
+			colLen = append(colLen, types.UnspecifiedLength)
+			retCols = append(retCols, partCols[i])
+		}
 	}
-	return partCols, colLen
+	return retCols, colLen
 }
 
 func (s *PartitionProcessor) getUsedHashPartitions(ctx base.PlanContext,
@@ -247,16 +254,15 @@ func (s *PartitionProcessor) getUsedHashPartitions(ctx base.PlanContext,
 			used = []int{FullRange}
 			break
 		}
-		if !r.HighVal[0].IsNull() {
-			if len(r.HighVal) != len(partCols) {
-				used = []int{-1}
-				break
-			}
+
+		// The code below is for the range `r` is a point.
+		if len(r.HighVal) != len(partCols) {
+			used = []int{FullRange}
+			break
 		}
-		highLowVals := make([]types.Datum, 0, len(r.HighVal)+len(r.LowVal))
-		highLowVals = append(highLowVals, r.HighVal...)
-		highLowVals = append(highLowVals, r.LowVal...)
-		pos, isNull, err := hashExpr.EvalInt(ctx.GetExprCtx().GetEvalCtx(), chunk.MutRowFromDatums(highLowVals).ToRow())
+		vals := make([]types.Datum, 0, len(partCols))
+		vals = append(vals, r.HighVal...)
+		pos, isNull, err := hashExpr.EvalInt(ctx.GetExprCtx().GetEvalCtx(), chunk.MutRowFromDatums(vals).ToRow())
 		if err != nil {
 			// If we failed to get the point position, we can just skip and ignore it.
 			continue