SELECT DISTINCT

i have an application intended to allow someone to look at an image file,
and enter data about the subject of the image. the application puts up a
copy of the image, and them provides fields for the user to fill in. the
combo boxes are preloaded with the data that has been seen before (like
model numbers). i am generating a web page, and using C for the
application, running on PGSQL 7.2 on a Lunix 7.2 (RH) system.

so far, the application seems to work fine, when it works. occasionally, it
seems to fail after a call to the database of SELECT DISTINCT, which i use
to preload the combo boxes. usually it fails during the same call each time
thru (looking for the same column), but occasionally it fails somewhere
else. reloading the page sometimes cures the problem, but sometimes not.

the application is not leaving me any pearls of wisdom in the syslog file,
and the process is not hung up.

i am sure it is something stupid i am doing.

this is the string i am using to query the database:

#define DBGSTRING "SELECT DISTINCT %s FROM %s ;\n"

any help would be appreciated, i have been hitting this wall for about
three weeks, and working around it, but i need to get things settled down
soon, so i need to deal with it.

thanx

stev knowles