Try this. The date '01-01-1970 08:00' corrects for my time zone which is UTF+8 - please adjust for wherever you are. And of course this doesn't adjust for Daylight Saving if it applies in your location (my state decided some years ago that Daylight Saving was too disruptive for milking cows, so we don't do it!).
use mdb;
go
select CO.chg_ref_num
,dateadd(s,CO.start_date, '01-01-1970 08:00') as chg_start_date
,dateadd(s,CO.close_date, '01-01-1970 08:00') as chg_end_date
,CA.description
,dateadd(s,CA.time_stamp, '01-01-1970 08:00') as alg_timestamp
,CC.last_name, CC.first_name
from chg CO left join chgalg CA on CO.id = CA.change_id
left join ca_contact CC on CA.analyst = CC.contact_uuid
;
go
Regards,
James