Just to flag, that I could not load a table into Postgres using the DB Loader node (Knime 4.7.7), because a UUID (GUID) field (type ‘string’ in Knime, type ‘uuid’ in Postgres [reported as OTHER in Knime console message]) could not be mapped in the Output Type Mapping tab (‘string’ can only be mapped to several types of CHAR/VARCHAR, but not to OTHER).
Adding the JDBC parameter stringtype=unspecified (as per here: Errors writing KNIME string to PostgreSQL uuid field and here: Insert GUID value into Postgresql database table) did not solve the problem, though it did allow me to successfully use the DB Insert node instead. Maybe something needs to be tweaked in the DB Loader node?