Re: Discrepancy in query output

My following query sometimes gives 72 rows and sometimes gives 71 rows as output. How could it misses one?

SELECT distinct on (st.gid) sv.timing, st.gid, st.area

FROM servers sv

INNER JOIN sites st

ON (st_distance(sv.geom, st.geom)<8.5) where

        sv.workmode = 1 AND sv.timing >= timestamp '2018-02-02 00:00:00' 

    and sv.timing <= timestamp '2018-02-02 23:59:59'