diff --git a/main.go b/main.go
index 3fd42ff2..11929ce1 100644
--- a/main.go
+++ b/main.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
+	"strings"
 	"time"
 )
 
@@ -287,7 +288,9 @@ func (s *DB) Raw(sql string, values ...interface{}) *DB {
 
 func (s *DB) Exec(sql string, values ...interface{}) *DB {
 	scope := s.clone().NewScope(nil)
-	scope.Raw(scope.buildWhereCondition(map[string]interface{}{"query": sql, "args": values}))
+	generatedSql := scope.buildWhereCondition(map[string]interface{}{"query": sql, "args": values})
+	generatedSql = strings.TrimSuffix(strings.TrimPrefix(generatedSql, "("), ")")
+	scope.Raw(generatedSql)
 	return scope.Exec().db
 }
 
diff --git a/mysql.go b/mysql.go
index 666bb0aa..9635507e 100644
--- a/mysql.go
+++ b/mysql.go
@@ -38,7 +38,7 @@ func (d *mysql) SqlTag(value reflect.Value, size int) string {
 		}
 	case reflect.Struct:
 		if value.Type() == timeType {
-			return "timestamp"
+			return "timestamp NULL"
 		}
 	default:
 		if _, ok := value.Interface().([]byte); ok {
diff --git a/scope_private.go b/scope_private.go
index 2d5f3ff4..b3439c57 100644
--- a/scope_private.go
+++ b/scope_private.go
@@ -23,7 +23,7 @@ func (scope *Scope) buildWhereCondition(clause map[string]interface{}) (str stri
 		if regexp.MustCompile("^\\s*\\d+\\s*$").MatchString(value) {
 			id, _ := strconv.Atoi(value)
 			return scope.primaryCondiation(scope.AddToVars(id))
-		} else {
+		} else if value != "" {
 			str = fmt.Sprintf("(%v)", value)
 		}
 	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64:
@@ -300,7 +300,7 @@ func (s *Scope) joinsSql() string {
 
 func (scope *Scope) prepareQuerySql() {
 	if scope.Search.Raw {
-		scope.Raw(strings.TrimLeft(scope.CombinedConditionSql(), "WHERE "))
+		scope.Raw(strings.TrimRight(strings.TrimLeft(scope.CombinedConditionSql(), "WHERE ("), ")"))
 	} else {
 		scope.Raw(fmt.Sprintf("SELECT %v %v FROM %v %v", scope.topSql(), scope.selectSql(), scope.QuotedTableName(), scope.CombinedConditionSql()))
 	}