I found out that the database reader always converts Integer columns as Decimal (I'm using an Oracle 10g Database).
Consequently, Integers are always converted like this :
DB ID KNIME ID
This is quite annoying when trying to use them in the joiner, as your data is not formatted as you wanted it to be...
Maybe would it be useful to let the user manually define the column type (Integer, Decimal) of the data extracted from a database ? This feature is actually available in the file Reader, but not in the database reader.