SQL joining same columns in different ways - sql-server

Question

select top 1000
f.*, s.TimeZoneCode as TimeZoneOrigin,
s2.TimeZoneCode as TimeZoneDestination,
tz.StandardVariation as VariationOrigin,
tz2.StandardVariation as VariationDestination,
tzv.Variation as TimeVariation,
tzv2.Variation as TimeVariation2
from
REZNVWB01.MIT.HVResearchDataSetDraft1 f
inner join
REZNVOD01.dbo.Station s on s.StationCode = f.TripOriginLocationCode
inner join
REZNVOD01.dbo.Station s2 on s2.StationCode = f.TripDestinationLocationCode
inner join
REZNVOD01.dbo.TimeZone tz on tz.TimeZoneCode = s.TimeZoneCode
inner join
REZNVOD01.dbo.TimeZone tz2 on tz2.TimeZoneCode = s.TimeZoneCode
inner join
REZNVOD01.dbo.TimeZoneVariation tzv on tzv.TimeZoneCode = s.TimeZoneCode
and tzv.EndUTC >= BookingDate
and tzv.StartUTC <= BookingDate
I have one table with StartUTC and EndUTC and timezonevariation for each row. I want to look at BookingTime, and gain the timezonevariation for when bookingtime is between StartUTC and EndUTC.
What do I need to change in this code?
inner join
REZNVOD01.dbo.TimeZoneVariation tzv on tzv.TimeZoneCode = s.TimeZoneCode
and tzv.EndUTC >= BookingDate
and tzv.StartUTC <= BookingDate
Is this code correct if the TimeZoneVariation code StartUTC and EndUTC are between conditions (IE startUTC might be 5:00 and endUTC might be 10:00, I want the TimeZoneVariation value where BookingDate is between startUTC and endUTC)

Answer 1

To answer your first question - merely by the logic - you can use the BETWEEN statement that could make your intent clearer. BETWEEN is inclusive, which means it includes the values at either end of the range in the comparison:
INNER JOIN REZNVOD01.dbo.TimeZoneVariation tzv
ON tzv.TimeZoneCode = s.TimeZoneCode AND
BookingDate BETWEEN tzv.EndUTC AND tzv.StartUTC
However, you're not clarifying whether "BookingDate" is a field within "f" or a variable. If it's a variable, make sure you prepend it with the commercial at (#) and if it's from "f", please declare it as such (E.G. f.BookingDate). This practice will make your code clearer to those reading it.
As to your final query ... it might be beneficial to spell out your table aliases instead of abbreviating them so much (I like to break my lines down and do indentation to help visualize the join relationships):
SELECT TOP 1000
f.*,
origStation.TimeZoneCode AS TimeZoneOrigin,
destStation.TimeZoneCode AS TimeZoneDestination,
origTz.StandardVariation AS VariationOrigin,
destTz.StandardVariation AS VariationDestination,
origTzv.Variation AS TimeVariationOrigin,
destTzv.Variation AS TimeVariationDestination
FROM
REZNVWB01.MIT.HVResearchDataSetDraft1 AS f
INNER JOIN REZNVOD01.dbo.Station AS origStation
ON origStation.StationCode=f.TripOriginLocationCode
INNER JOIN REZNVOD01.dbo.Station AS destStation
ON destStation.StationCode=f.TripDestinationLocationCode
INNER JOIN REZNVOD01.dbo.TimeZone AS origTz
ON origTz.TimeZoneCode=origStation.TimeZoneCode
INNER JOIN REZNVOD01.dbo.TimeZone AS destTz
ON destTz.TimeZoneCode=destStation.TimeZoneCode
INNER JOIN REZNVOD01.dbo.TimeZoneVariation AS origTzv
ON origTzv.TimeZoneCode = origStation.TimeZoneCode AND
f.BookingDate BETWEEN origTzv.EndUTC AND origTzv.StartUTC
INNER JOIN REZNVOD01.dbo.TimeZoneVariation AS destTzv
ON destTzv.TimeZoneCode = destStation.TimeZoneCode AND
f.BookingDate BETWEEN destTzv.EndUTC AND destTzv.StartUTC
I don't quite understand your last question. Could you please restate it?
Thanks!