pyodbc: No result for SQL-select if character field in where-clause does not match in length using parameter (ORACLE)

Hello,

I am using PyODBC 4.0.14 with Python 3.4.4 on Windows 7 64-Bit and connect to a Oracle 11gR2 database running on a SLES12 machine. The ODBC Driver I am using comes with the Client installation of Oracle: 11.02.00.01

When I execute a select-Statement that contains a string parameter (NCHAR in Oracle) I do not get any results if the length of the parameter and the length of the database field do not exactly match.

See this minimal example:

""" create table foo
    (
        colnum    number(20)    not null,
        colchar1  nchar(6)      not null,
        colchar2  nchar(20)     not null
    );

    insert into foo values (1, 'foobar', 'foobar');
"""

import pyodbc

conn = pyodbc.connect("...")
curs = conn.cursor()


curs.execute("select * from foo;")
print(curs.fetchall()) # Works

curs.execute("select * from foo where colnum = ? and colchar1 = ?;", [ 1, "foobar"] )
print(curs.fetchall()) # Works

curs.execute("select * from foo where colnum = ? and colchar2 = ?;", [ 1, "foobar"] )
print(curs.fetchall()) # Does not work

curs.execute("select * from foo where colnum = ? and colchar2 = ?;", [ 1, "foobar".ljust(20) ] )
print(curs.fetchall()) # Works

This does only happen for Oracle Databases. I have tested this with Postgres 9.6.2 and the issue does not come up. I have yet to test this on a Linux machine and maybe try Oracle 12c - but I don’t expect changes.