distsql: support pushing isnull down (pingcap#2069)

distsql/xeval/eval.go

@@ -75,6 +75,8 @@ func (e *Evaluator) Eval(expr *tipb.Expr) (types.Datum, error) {
 		return e.evalControlFuncs(expr)
 	case tipb.ExprType_Coalesce:
 		return e.evalCoalesce(expr)
+	case tipb.ExprType_IsNull:
+		return e.evalIsNull(expr)
 	}
 	return types.Datum{}, nil
 }
@@ -94,3 +96,17 @@ func (e *Evaluator) evalTwoChildren(expr *tipb.Expr) (left, right types.Datum, e
 	}
 	return
 }
+
+func (e *Evaluator) evalIsNull(expr *tipb.Expr) (types.Datum, error) {
+	if len(expr.Children) != 1 {
+		return types.Datum{}, ErrInvalid.Gen("ISNULL need 1 operand, got %d", len(expr.Children))
+	}
+	d, err := e.Eval(expr.Children[0])
+	if err != nil {
+		return types.Datum{}, errors.Trace(err)
+	}
+	if d.IsNull() {
+		return types.NewIntDatum(1), nil
+	}
+	return types.NewIntDatum(0), nil
+}

distsql/xeval/eval_test.go

@@ -462,6 +462,39 @@ func (s *testEvalSuite) TestWhereIn(c *C) {
 	}
 }
 
+func (s *testEvalSuite) TestEvalIsNull(c *C) {
+	colID := int64(1)
+	row := make(map[int64]types.Datum)
+	row[colID] = types.NewIntDatum(100)
+	xevaluator := &Evaluator{Row: row}
+	null, trueAns, falseAns := types.Datum{}, types.NewIntDatum(1), types.NewIntDatum(0)
+	cases := []struct {
+		expr   *tipb.Expr
+		result types.Datum
+	}{
+		{
+			expr:   buildExpr(tipb.ExprType_IsNull, types.NewStringDatum("abc")),
+			result: falseAns,
+		},
+		{
+			expr:   buildExpr(tipb.ExprType_IsNull, null),
+			result: trueAns,
+		},
+		{
+			expr:   buildExpr(tipb.ExprType_IsNull, types.NewIntDatum(0)),
+			result: falseAns,
+		},
+	}
+	for _, ca := range cases {
+		result, err := xevaluator.Eval(ca.expr)
+		c.Assert(err, IsNil)
+		c.Assert(result.Kind(), Equals, ca.result.Kind())
+		cmp, err := result.CompareDatum(ca.result)
+		c.Assert(err, IsNil)
+		c.Assert(cmp, Equals, 0)
+	}
+}
+
 func inExpr(target interface{}, list ...interface{}) *tipb.Expr {
 	targetDatum := types.NewDatum(target)
 	var listDatums []types.Datum

plan/expr_to_pb.go

@@ -126,7 +126,7 @@ func scalarFuncToPBExpr(client kv.Client, expr *expression.ScalarFunction) *tipb
 		return logicalOpsToPBExpr(client, expr)
 	case ast.And, ast.Or, ast.BitNeg, ast.Xor, ast.LeftShift, ast.RightShift:
 		return bitwiseFuncToPBExpr(client, expr)
-	case ast.Case, ast.Coalesce, ast.If:
+	case ast.Case, ast.Coalesce, ast.If, ast.IsNull:
 		return builtinFuncToPBExpr(client, expr)
 	default:
 		return nil
@@ -363,7 +363,7 @@ func builtinFuncToPBExpr(client kv.Client, expr *expression.ScalarFunction) *tip
 	switch expr.FuncName.L {
 	case ast.Case, ast.If:
 		return controlFuncsToPBExpr(client, expr)
-	case ast.Coalesce:
+	case ast.Coalesce, ast.IsNull:
 		return otherFuncsToPBExpr(client, expr)
 	default:
 		return nil
@@ -375,6 +375,8 @@ func otherFuncsToPBExpr(client kv.Client, expr *expression.ScalarFunction) *tipb
 	switch expr.FuncName.L {
 	case ast.Coalesce:
 		tp = tipb.ExprType_Coalesce
+	case ast.IsNull:
+		tp = tipb.ExprType_IsNull
 	}
 	return convertToPBExpr(client, expr, tp)
 }

plan/logcial_plan_test.go

@@ -263,7 +263,7 @@ func supportExpr(exprType tipb.ExprType) bool {
 	case tipb.ExprType_Case, tipb.ExprType_If:
 		return true
 	// other functions
-	case tipb.ExprType_Coalesce:
+	case tipb.ExprType_Coalesce, tipb.ExprType_IsNull:
 		return true
 	case kv.ReqSubTypeDesc:
 		return true

plan/physical_plan_test.go

@@ -184,6 +184,11 @@ func (s *testPlanSuite) TestPushDownExpression(c *C) {
 			sql:  "a = coalesce(null, null, a, b)",
 			cond: "eq(test.t.a, coalesce(<nil>, <nil>, test.t.a, test.t.b))",
 		},
+		// isnull
+		{
+			sql:  "b is null",
+			cond: "isnull(test.t.b)",
+		},
 	}
 	for _, ca := range cases {
 		sql := "select * from t where " + ca.sql

store/localstore/local_client.go

@@ -80,7 +80,7 @@ func supportExpr(exprType tipb.ExprType) bool {
 	case tipb.ExprType_Case, tipb.ExprType_If:
 		return true
 	// other functions
-	case tipb.ExprType_Coalesce:
+	case tipb.ExprType_Coalesce, tipb.ExprType_IsNull:
 		return true
 	case kv.ReqSubTypeDesc:
 		return true