How to find the Nearest (day of the week) for a given date

Question

I been practicing queries, and my current scenario is to find the nearest Saturday for a given date. After i got the logic down, i came up with a, whats looks like a long and messy query. And I was wondering if there is a way to simplify this. Here's my query

DECLARE @DATE DATE
SET @DATE ='2013-09-13'

IF              DATENAME(DW,@DATE) = 'SUNDAY'
    BEGIN 
        SELECT  DATEADD(DAY,-1,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'MONDAY'
    BEGIN 
        SELECT  DATEADD(DAY,-2,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'TUESDAY'
    BEGIN 
        SELECT  DATEADD(DAY,-3,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'WEDNESDAY'
    BEGIN 
        SELECT  DATEADD(DAY,3,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'THURSDAY'
    BEGIN 
        SELECT  DATEADD(DAY,2,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'FRIDAY'
    BEGIN 
        SELECT  DATEADD(DAY,1,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'SATURDAY'
    BEGIN
        SELECT  CONVERT(NVARCHAR,@DATE) + ' IS SATURDAY' AS DATE_DOW
    END

As we can see the query is long and runs multiple IFs to look for TRUE condition. Please don't write the query, just hints. I would like to work on the query myself.

Answer 1

Here's my hint without answering, as you requested:

Consider date manipulation, using current date (you can use GETDATE() or your date variable), DATEADD() and DATEDIFF() can be used to write this in a couple lines.

If you just want to simplify your method you could use a CASE statement:

DECLARE @date DATE = '2013-09-13'
SELECT CASE WHEN DATENAME(DW,@DATE) = 'SUNDAY' THEN  CAST(DATEADD(DAY,-3,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'MONDAY' THEN CAST(DATEADD(DAY,-2,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'TUESDAY' THEN CAST(DATEADD(DAY,-1,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'WEDNESDAY' THEN CAST(DATEADD(DAY,1,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'THURSDAY' THEN CAST(DATEADD(DAY,2,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'FRIDAY' THEN CAST(DATEADD(DAY,3,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            ELSE CONVERT(NVARCHAR,@DATE) + ' IS SATURDAY'
       END

To clarify on the method I was hinting at and Sparky posted, you need to adjust DATEFIRST to make this work, it works for whichever day is the first day of the week, Saturday is the 7th day of the week, so:

SET DATEFIRST 7
DECLARE @date DATE = '2013-09-21'
SELECT DATEADD(day,7-DATEPART(weekday,@date),@date)

Answer 2

Try this:

select dateAdd(dd,7-DATEPART(dw,getDate()),GETDATE())

datePart(dw,...) returns day of the week for current date.

7 - that number , returns number of days until Saturday

Add the result to the date to get the next Saturday...

Similar logic if you need to go back to previous Saturday

Sql Fiddle: http://www.sqlfiddle.com/#!3/61998/2

Answer 3

Well not exactly an answer, but an alternative

    DECLARE @DATE DATE,
    @SUN DATE,
    @MON DATE,
    @TUE DATE,
    @WED DATE,
    @THU DATE,
    @FRI DATE,
    @SAT DATE

           SET @DATE = '2013-09-14'

    SET @SUN = DATEADD(DAY,-1,@DATE)
    SET @MON = DATEADD(DAY,-1,@DATE)
    SET @TUE = DATEADD(DAY,-2,@DATE)
    SET @WED = DATEADD(DAY,-3,@DATE)
    SET @THU = DATEADD(DAY,2,@DATE)
    SET @FRI = DATEADD(DAY,1,@DATE)
    SET @SAT = DATEADD(DAY,0,@DATE)

    SELECT CASE 
        WHEN DATENAME(DW,@DATE) = 'SUNDAY'
        THEN @SUN
        WHEN DATENAME(DW,@DATE) = 'MONDAY'
        THEN @MON
        WHEN DATENAME(DW,@DATE) = 'TUESDAY'
        THEN @TUE
        WHEN DATENAME(DW,@DATE) = 'WEDNESDAY'
        THEN @WED
        WHEN DATENAME(DW,@DATE) = 'THURSDAY'
        THEN @THU
        WHEN DATENAME(DW,@DATE) = 'FRIDAY'
        THEN @FRI
        ELSE @SAT
    END