diff --git a/evaluator/builtin_string.go b/evaluator/builtin_string.go
index ffa67b934d..d3656bec0d 100644
--- a/evaluator/builtin_string.go
+++ b/evaluator/builtin_string.go
@@ -275,12 +275,12 @@ func builtinSubstring(args []types.Datum, _ context.Context) (d types.Datum, err
 	}
 	pos := args[1].GetInt64()
 
-	length := int64(-1)
+	length, hasLen := int64(-1), false
 	if len(args) == 3 {
 		if args[2].Kind() != types.KindInt64 {
 			return d, errors.Errorf("Substring invalid pos args, need int but get %T", args[2].GetValue())
 		}
-		length = args[2].GetInt64()
+		length, hasLen = args[2].GetInt64(), true
 	}
 	// The forms without a len argument return a substring from string str starting at position pos.
 	// The forms with a len argument return a substring len characters long from string str, starting at position pos.
@@ -292,17 +292,20 @@ func builtinSubstring(args []types.Datum, _ context.Context) (d types.Datum, err
 	} else {
 		pos--
 	}
-	if pos > int64(len(str)) || pos <= int64(0) {
+	if pos > int64(len(str)) || pos < int64(0) {
 		pos = int64(len(str))
 	}
-	end := int64(len(str))
-	if length != int64(-1) {
-		end = pos + length
+	if hasLen {
+		if end := pos + length; end < pos {
+			d.SetString("")
+		} else if end > int64(len(str)) {
+			d.SetString(str[pos:])
+		} else {
+			d.SetString(str[pos:end])
+		}
+	} else {
+		d.SetString(str[pos:])
 	}
-	if end > int64(len(str)) {
-		end = int64(len(str))
-	}
-	d.SetString(str[pos:end])
 	return d, nil
 }
 
diff --git a/evaluator/builtin_string_test.go b/evaluator/builtin_string_test.go
index b5d598b1b6..fea7e0d829 100644
--- a/evaluator/builtin_string_test.go
+++ b/evaluator/builtin_string_test.go
@@ -263,6 +263,11 @@ func (s *testEvaluatorSuite) TestReplace(c *C) {
 
 func (s *testEvaluatorSuite) TestSubstring(c *C) {
 	defer testleak.AfterTest(c)()
+
+	d, err := builtinSubstring(types.MakeDatums([]interface{}{"hello", 2, -1}...), nil)
+	c.Assert(err, IsNil)
+	c.Assert(d.GetString(), Equals, "")
+
 	tbl := []struct {
 		str    string
 		pos    int64
@@ -271,10 +276,21 @@ func (s *testEvaluatorSuite) TestSubstring(c *C) {
 	}{
 		{"Quadratically", 5, -1, "ratically"},
 		{"foobarbar", 4, -1, "barbar"},
-		{"Quadratically", 5, 6, "ratica"},
+		{"Sakila", 1, -1, "Sakila"},
+		{"Sakila", 2, -1, "akila"},
 		{"Sakila", -3, -1, "ila"},
 		{"Sakila", -5, 3, "aki"},
 		{"Sakila", -4, 2, "ki"},
+		{"Quadratically", 5, 6, "ratica"},
+		{"Sakila", 1, 4, "Saki"},
+		{"Sakila", -6, 4, "Saki"},
+		{"Sakila", 2, 1000, "akila"},
+		{"Sakila", -5, 1000, "akila"},
+		{"Sakila", 2, -2, ""},
+		{"Sakila", -5, -2, ""},
+		{"Sakila", 2, 0, ""},
+		{"Sakila", -5, -3, ""},
+		{"Sakila", -1000, 3, ""},
 		{"Sakila", 1000, 2, ""},
 		{"", 2, 3, ""},
 	}