ODBC SELECT WHERE a IN ('frob') returns where a = '' too

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POSTGRESQL BUG REPORT TEMPLATE
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Your name               : Adam Haberlach
Your email address      : adam@be.com


System Configuration
---------------------
  Architecture (example: Intel Pentium)         : Intel Pentium

  Operating System (example: Linux 2.0.26 ELF)  :Linux version 2.2.2

  PostgreSQL version (example: PostgreSQL-6.5.1):   PostgreSQL-7.0

  Compiler used (example:  gcc 2.8.0)           : gcc version 2.7.2.3


Please enter a FULL description of your problem:
------------------------------------------------

When I do a query of the form

SELECT a FROM tbl WHERE a IN ('frob');

where a is an indexed text field containing 'frob', 'dingus', '', and
NULL

I get a set that includes rows both where
a == 'frob'
a == ''

This happens when I use ODBC from Microsoft Access's pass-through, but
does not seem to happen from the psql
command-line.  This seems to confuse my coworker who is more familiar
with non-Postgres databases then I.


--
Adam Haberlach             |"You have to understand that the
adam@newsnipple.com        |  entire 'Net is based on people with
http://www.newsnipple.com/ |  too much free time on their hands."