In order to connect to external databases, PostgreSQL supports Foreign Data Wrappers (FDW), and there are already many FDWs. However, among of FDWs have various restrictions preventing utilization of external databases features. As such a restriction, FDWs for schemaless databases need to change the foreign table definition, when some columns are added in remote database. This restriction can not take full advantage of the schemaless feature. In this time, we considered implementing FDW that does not require changing the external table when columns are added on external database. I would like to introduce this study based on the time-series database InfluxDB as schemaless database.