SQL GROUP BY or JOIN - sql

Question

I am using SQL 2008 and just cannot get this query to work. I have a table with flight price details in it. There are many rows for each day for each route and I want to return the lowest price per day for the route and also the DateAdded (the datetime that the row was added). I am almost there as I seem to have managed to get the lowest price per day returned but I can't seem to get the correct dateadded to be returned. The code below seems to work to return the lowest price per day but I think I need some sort of join to also return the DateAdded?
ALTER PROCEDURE [dbo].[FlightInfoLowestPricePerDay]
(
#AirportFrom varchar(5),
#AirportTo varchar(5)
)
AS
select DATEADD(dd, 0, DATEDIFF(dd, 0, TimeDeparture)) as FlightDate, MIN(Price) as MinPrice
from FlightInfo
where AirportFrom = #AirportFrom and AirportTo = #AirportTo
AND TimeDeparture > DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))
Group By DATEADD(dd, 0, DATEDIFF(dd, 0, TimeDeparture))
Order by FlightDate ASC
I have tried things such as the code below but I do not fully understand joins yet so have been struggling for quite a while although I'm sure I'm missing something very simple!
ALTER PROCEDURE [dbo].[FlightInfoLowestPricePerDay]
(
#AirportFrom varchar(5),
#AirportTo varchar(5)
)
AS
select DATEADD(dd, 0, DATEDIFF(dd, 0, fi1.TimeDeparture)) as FlightDate, MIN(fi1.Price) as MinPrice, fi2.DateAdded
from FlightInfo
fi1 join FlightInfo fi2 on fi1.Price = fi2.Price
where fi1.AirportFrom = #AirportFrom and fi1.AirportTo = #AirportTo
AND fi1.TimeDeparture > DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))
Group By DATEADD(dd, 0, DATEDIFF(dd, 0, fi1.TimeDeparture))
Order by FlightDate ASC

Answer 1

Add fi2.DateAdded in Group By
ALTER PROCEDURE [dbo].[FlightInfoLowestPricePerDay]
(
#AirportFrom varchar(5),
#AirportTo varchar(5)
)
AS
select DATEADD(dd, 0, DATEDIFF(dd, 0, fi1.TimeDeparture)) as FlightDate, MIN(fi1.Price) as MinPrice, Cast(Convert(varchar(20),fi2.DateAdded,101) as datetime) DateAdded
from FlightInfo
fi1 join FlightInfo fi2 on fi1.Price = fi2.Price
where fi1.AirportFrom = #AirportFrom and fi1.AirportTo = #AirportTo
AND fi1.TimeDeparture > DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))
Group By DATEADD(dd, 0, DATEDIFF(dd, 0, fi1.TimeDeparture)),Cast(Convert(varchar(20),fi2.DateAdded,101) as datetime)
Order by FlightDate ASC

Answer 2

OK I decided to simplify it a bit as I've wasted too much time on this already so now I am passing a specific date into the query and running the query multiple times to get the results I need:
ALTER PROCEDURE [dbo].[FlightInfoLowestPriceDateAddedForSpecificDate]
(
#AirportFrom varchar(5),
#AirportTo varchar(5),
#Date datetime
)
AS
select top 1 *
from FlightInfo
where AirportFrom = #AirportFrom and AirportTo = #AirportTo
AND DATEADD(dd, 0, DATEDIFF(dd, 0, TimeDeparture)) = DATEADD(dd, 0, DATEDIFF(dd, 0, #Date))
Order by Price asc

Answer 3

You want to use window function for this. One way is with row_number():
select flightDate, price
from (select DATEADD(dd, 0, DATEDIFF(dd, 0, TimeDeparture)) as FlightDate, fi.*,
ROW_NUMBER() over (partition by airportFrom, airportTo, DATEADD(dd, 0, DATEDIFF(dd, 0, TimeDeparture)) order by price) as seqnum
from FlightInfo fi
where AirportFrom = #AirportFrom and AirportTo = #AirportTo and
TimeDeparture > DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))
) fi
where seqnum = 1
If you are using more recent versions of SQL Server, then you can take advantage of the date data type:
select flightDate, price
from (select cast(TimeDeparture as date) as FlightDate, fi.*,
ROW_NUMBER() over (partition by airportFrom, airportTo, cast(TimeDeparture as date) order by price) as seqnum
from FlightInfo fi
where AirportFrom = #AirportFrom and AirportTo = #AirportTo and
TimeDeparture > cast(getdate() as date)
) fi
where seqnum = 1

Answer 4

You can two sub queries (one that gets the small prices per day and the second one the DateAdded)
SELECT f1.FlightDate, f1.MinPrice, f2.DateAdded From
(
SELECT
DATEADD(dd, 0, DATEDIFF(dd, 0, fi1.TimeDeparture)) as FlightDate,
MIN(fi1.Price) as MinPrice
FROM FlightInfo fi1
WHERE fi1.AirportFrom = #AirportFrom and fi1.AirportTo = #AirportTo
AND fi1.TimeDeparture > DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))
Group By
DATEADD(dd, 0, DATEDIFF(dd, 0, fi1.TimeDeparture))
) f1
INNER JOIN
(
SELECT DISTINCT
DATEADD(dd, 0, DATEDIFF(dd, 0, fi2.DateAdded)) AS DateAdded,
Price FROM FlightInfo fi2
WHERE fi2.AirportFrom = #AirportFrom and fi2.AirportTo = #AirportTo
AND fi2.TimeDeparture > DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))
) f2 ON f2.Price = f1.MinPrice