Find closest date in SQL Server - sql

Question

I have a table dbo.X with DateTime column Y which may have hundreds of records.
My Stored Procedure has parameter #CurrentDate, I want to find out the date in the column Y in above table dbo.X which is less than and closest to #CurrentDate.
How to find it?

Answer 1

The where clause will match all rows with date less than #CurrentDate and, since they are ordered descendantly, the TOP 1 will be the closest date to the current date.
SELECT TOP 1 *
FROM x
WHERE x.date < #CurrentDate
ORDER BY x.date DESC

Answer 2

Use DateDiff and order your result by how many days or seconds are between that date and what the Input was
Something like this
select top 1 rowId, dateCol, datediff(second, #CurrentDate, dateCol) as SecondsBetweenDates
from myTable
where dateCol < #currentDate
order by datediff(second, #CurrentDate, dateCol)

Answer 3

I have a better solution for this problem i think.
I will show a few images to support and explain the final solution.
Background
In my solution I have a table of FX Rates. These represent market rates for different currencies. However, our service provider has had a problem with the rate feed and as such some rates have zero values. I want to fill the missing data with rates for that same currency that as closest in time to the missing rate. Basically I want to get the RateId for the nearest non zero rate which I will then substitute. (This is not shown here in my example.)
1) So to start off lets identify the missing rates information:
Query showing my missing rates i.e. have a rate value of zero
2) Next lets identify rates that are not missing.
Query showing rates that are not missing
3) This query is where the magic happens. I have made an assumption here which can be removed but was added to improve the efficiency/performance of the query. The assumption on line 26 is that I expect to find a substitute transaction on the same day as that of the missing / zero transaction.
The magic happens is line 23: The Row_Number function adds an auto number starting at 1 for the shortest time difference between the missing and non missing transaction. The next closest transaction has a rownum of 2 etc.
Please note that in line 25 I must join the currencies so that I do not mismatch the currency types. That is I don't want to substitute a AUD currency with CHF values. I want the closest matching currencies.
Combining the two data sets with a row_number to identify nearest transaction
4) Finally, lets get data where the RowNum is 1
The final query
The query full query is as follows;
; with cte_zero_rates as
(
Select *
from fxrates
where (spot_exp = 0 or spot_exp = 0)
),
cte_non_zero_rates as
(
Select *
from fxrates
where (spot_exp > 0 and spot_exp > 0)
)
,cte_Nearest_Transaction as
(
select z.FXRatesID as Zero_FXRatesID
,z.importDate as Zero_importDate
,z.currency as Zero_Currency
,nz.currency as NonZero_Currency
,nz.FXRatesID as NonZero_FXRatesID
,nz.spot_imp
,nz.importDate as NonZero_importDate
,DATEDIFF(ss, z.importDate, nz.importDate) as TimeDifferece
,ROW_NUMBER() Over(partition by z.FXRatesID order by abs(DATEDIFF(ss, z.importDate, nz.importDate)) asc) as RowNum
from cte_zero_rates z
left join cte_non_zero_rates nz on nz.currency = z.currency
and cast(nz.importDate as date) = cast(z.importDate as date)
--order by z.currency desc, z.importDate desc
)
select n.Zero_FXRatesID
,n.Zero_Currency
,n.Zero_importDate
,n.NonZero_importDate
,DATEDIFF(s, n.NonZero_importDate,n.Zero_importDate) as Delay_In_Seconds
,n.NonZero_Currency
,n.NonZero_FXRatesID
from cte_Nearest_Transaction n
where n.RowNum = 1
and n.NonZero_FXRatesID is not null
order by n.Zero_Currency, n.NonZero_importDate