query problems

[Brad]

Hi,
I'm having a problem with a query I'm sending. I have a table of GIS data containing columns:

id INT PRIMARY KEY NOT NULL AUTO INCREMENT
long FLOAT NOT NULL
lat FLOAT NOT NULL
winWeibC FLOAT NOT NULL
winWeibK FLOAT NOT NULL
etc...

I have about 7.5 million fields in the table and want to query one entry based on latitude and longitude. When I execute the query using the following script I get an empty set:

SELECT winWeibK FROM my_DB WHERE lat=31.018 AND long=-111.197;

However, when I send the following query I get a successful result:

SELECT winWeibK FROM my_DB WHERE id=7642;

This doesn't help me though since I don't know the correct id number, I only know the latitude and longitude. Any idea why I'm getting an empty set on my composite query? If it helps, I also had the idea of doing "SELECT * FROM my_DB WHERE lat=31.018", then querying those results for the longitude, but got an empty set from the above quoted query so I couldn't even try a second query.

Basically it'll only let me query with the primark key. Is that normal? If so, how do I get around it?

Thanks