Problemas using "Unique Table" in PostgreSQL

Working with SQL Server i havent any problem. But i start to work with 
PostreSQL and now i cannot update ADO.Recordset when de SELECT - SQL join 
other tables than de Principal or Updateable table.

The Select used is the following

SELECT unidroga.*, drogas.descrip AS NameDroga FROM unidroga INNER JOIN 
drogas ON unidroga.droga = drogas.coddroga WHERE (unidroga.articulo = 
'_838394932')

and i use this to update only the table unidroga.

oAdoRS.Properties("Unique Table").Value = "unidroga"

This works with SQL - SERVER but doesnt work with PostgreSQL, anyone can 
help me???

Fabián.