Uitleg van deze query

Kan iemand mij uitleggen wat deze query precies doet? Het is van MsSql2000

declare @t table(RecordID int, SampleTime datetime)
insert @t
select RecordID, SampleTime From Test

Select RecordID, Sampletime = (Select top 1 sampletime
from @t
where abs(datediff(s, sampletime, b.sampletime )) <> 0
order by abs(datediff(s, sampletime, b.sampletime )))
from @t b