* changed type properties for timestamp

include/cpphibernate/driver/mariadb/helper/type_properties.h

@@ -330,7 +330,7 @@ beg_namespace_cpphibernate_driver_mariadb
     struct type_properties<timestamp, void>
     {
         static constexpr decltype(auto) type()
-            { return "DATETIME"; }
+            { return "BIGINT"; }
 
         static inline timestamp convert_to(const value_t& value)
             { return timestamp(utl::from_string<uint64_t>(*value)); }
@@ -339,16 +339,16 @@ beg_namespace_cpphibernate_driver_mariadb
             { return utl::to_string(static_cast<uint64_t>(value)); }
 
         static constexpr const char* convert_to_open()
-            { return "FROM_UNIXTIME("; }
+            { return nullptr; }
 
         static constexpr const char* convert_to_close()
-            { return ")"; }
+            { return nullptr; }
 
         static constexpr const char* convert_from_open()
-            { return "UNIX_TIMESTAMP("; }
+            { return nullptr; }
 
         static constexpr const char* convert_from_close()
-            { return ")"; }
+            { return nullptr; }
     };
 
     template<>