The following bug has been logged online:
Bug reference: 1904
Logged by: Brian Cox
Email address: bcox(at)timestock(dot)com
PostgreSQL version: 8.0.3
Operating system: Linux (Fedora Core 2)
Description: using distinct with null col causes error
Details:
any_db=> create view view1 as select null as col1 from any_table;
CREATE VIEW
any_db=> select distinct col1 from view1;
ERROR: failed to find conversion function from "unknown" to text