Use ordered index with is null predicate

Author: ari-e

pkg/planner/core/casetest/index/BUILD.bazel

@@ -9,7 +9,7 @@ go_test(
     ],
     data = glob(["testdata/**"]),
     flaky = True,
-    shard_count = 5,
+    shard_count = 6,
     deps = [
         "//pkg/testkit",
         "//pkg/testkit/testdata",

pkg/planner/core/casetest/index/index_test.go

@@ -209,3 +209,15 @@ func TestRangeIntersection(t *testing.T) {
 		tk.MustQuery(sql).Sort().Check(testkit.Rows(output[i].Result...))
 	}
 }
+
+func TestOrderedIndexWithIsNull(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("CREATE TABLE t1 (a int key, b int, c int, index (b, c));")
+	tk.MustQuery("explain select a from t1 where b is null order by c").Check(testkit.Rows(
+		"Projection_6 10.00 root  test.t1.a",
+		"└─IndexReader_12 10.00 root  index:IndexRangeScan_11",
+		"  └─IndexRangeScan_11 10.00 cop[tikv] table:t1, index:b(b, c) range:[NULL,NULL], keep order:true, stats:pseudo",
+	))
+}

pkg/util/ranger/detacher.go

@@ -182,6 +182,16 @@ func getPotentialEqOrInColOffset(sctx *rangerctx.RangerContext, expr expression.
 				return i
 			}
 		}
+	case ast.IsNull:
+		c, ok := f.GetArgs()[0].(*expression.Column)
+		if !ok {
+			return -1
+		}
+		for i, col := range cols {
+			if col.EqualColumn(c) {
+				return i
+			}
+		}
 	}
 	return -1
 }
@@ -635,27 +645,34 @@ func allEqOrIn(expr expression.Expression) bool {
 			}
 		}
 		return true
-	case ast.EQ, ast.NullEQ, ast.In:
+	case ast.EQ, ast.NullEQ, ast.In, ast.IsNull:
 		return true
 	}
 	return false
 }
 
 func extractValueInfo(expr expression.Expression) *valueInfo {
-	if f, ok := expr.(*expression.ScalarFunction); ok && (f.FuncName.L == ast.EQ || f.FuncName.L == ast.NullEQ) {
-		getValueInfo := func(c *expression.Constant) *valueInfo {
-			mutable := c.ParamMarker != nil || c.DeferredExpr != nil
-			var value *types.Datum
-			if !mutable {
-				value = &c.Value
+	if f, ok := expr.(*expression.ScalarFunction); ok {
+		if f.FuncName.L == ast.IsNull {
+			val := &types.Datum{}
+			val.SetNull()
+			return &valueInfo{value: val, mutable: false}
+		}
+		if f.FuncName.L == ast.EQ || f.FuncName.L == ast.NullEQ {
+			getValueInfo := func(c *expression.Constant) *valueInfo {
+				mutable := c.ParamMarker != nil || c.DeferredExpr != nil
+				var value *types.Datum
+				if !mutable {
+					value = &c.Value
+				}
+				return &valueInfo{value, mutable}
+			}
+			if c, ok := f.GetArgs()[0].(*expression.Constant); ok {
+				return getValueInfo(c)
+			}
+			if c, ok := f.GetArgs()[1].(*expression.Constant); ok {
+				return getValueInfo(c)
 			}
-			return &valueInfo{value, mutable}
-		}
-		if c, ok := f.GetArgs()[0].(*expression.Constant); ok {
-			return getValueInfo(c)
-		}
-		if c, ok := f.GetArgs()[1].(*expression.Constant); ok {
-			return getValueInfo(c)
 		}
 	}
 	return nil
@@ -714,8 +731,12 @@ func ExtractEqAndInCondition(sctx *rangerctx.RangerContext, conditions []express
 		if ma == nil {
 			if accesses[i] != nil {
 				if allEqOrIn(accesses[i]) {
-					newConditions = append(newConditions, accesses[i])
 					columnValues[i] = extractValueInfo(accesses[i])
+					if columnValues[i] != nil && columnValues[i].value != nil && columnValues[i].value.IsNull() {
+						accesses[i] = nil
+					} else {
+						newConditions = append(newConditions, accesses[i])
+					}
 				} else {
 					accesses[i] = nil
 				}