Find closest date in SQL Server

Question

I have a table dbo.X with DateTime column Y which may have hundreds of records.

My Stored Procedure has parameter @Curre

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

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

Answer 3

CREATE PROCEDURE CurrentDate
@CurrentDate DATETIME
AS
BEGIN
    Select * from orders
    where OrderDate < @CurrentDate
END
GO

Answer 4

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)