[postgis-users] Weird behavior - Contains function

[cyw at dls.net]

Hi All,

I have a two geo tables:
    county - contains polygons of counties for a state
    road - all road segments for a state

I tried to delete all the road segments that are not in a specific county 
(porter) with this sql:
    delete from road where NOT Contains((select the_geom from county where 
polygon_nm='porter'), the_geom)

When I examined the results, I found that some segments in the middle of the 
county polygon also got deleted. I noticed these wrongly deleted segments 
when I saw gaps in some roads in a map display. These segments are not long 
ones that would span across the county.

Thanks,
CYW