Datediff for each row agaimst maximum row

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Hello,

I have a SQL table where i have a date column and it has the following format 1yymmdd. I have converted this to datetime using following sql query.

Cast(left(right(ltrim(str(date,25,5)), LEN(ltrim(str(date,25,5)))-3),2) +'-' + left(right(ltrim(str(date,25,5)), LEN(ltrim(str(date,25,5)))-5),2) +'-' +
left(right(ltrim(str(date,25,5)), LEN(ltrim(str(date,25,5)))-1),2) as datetime)

The above query gives me date in following format YYYY-MM-DD HH:MM:SS.
But the confusion is i want to calculate the datedifference of each row with maximum date that the query returns.

For Example:

If i run the query and it returns the following 3 dates
2016-06-08 00:00:00.000
2016-06-05 00:00:00.000
2016-06-03 00:00:00.000

So in above result set the highest date is 2016-06-08 00:00:00.000 and when i calculate the difference between it and other 2 days it should return 3 and 5 days respectively,
so what i want is to calculate the difference between the max date and every other date and select only the dates which has difference of less than 3 dayys.

I am looking forward to your help as always. Thanks alot.

What I have tried:

Googled it and could not find any exact situation

Posted 30-Nov-16 19:04pm

Faran Saleem

Updated 1-Dec-16 0:49am

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jamuro77 · Answer 1 · 2016-12-01T00:48:00

Solution 2

Well,

1) To put days in positive you only have to take absolute value or switching the order of date values in datediff function.

2) To filter values you should use a Common Table Expression and then filter.

Here is the code:

;with cte as (select OrderDate, datediff(day,OrderDate,MAX(OrderDate) over()) as Days from sales)
select * from cte
where Days between 1 and 6
order by OrderDate desc

Posted 1-Dec-16 0:48am

jamuro77

Updated 1-Dec-16 0:54am

v2

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Faran Saleem 2-Dec-16 2:04am

But i am already using CTE..Using them because i had to compare each row with the previous value.

So how can i do it?

jamuro77 · Answer 2 · 2016-11-30T20:15:00

Solution 1

Hi, the solution is easy. You just have to use a "SQL Windowing function". Anyway, have a look to SQL Documentation.

Let's suppose we have a table with a "OrderDate" field. The query to get what you want would be:

select OrderDate, datediff(day,MAX(OrderDate) over(),OrderDate) from sales
order by OrderDate desc

Note, "over" operator above in the query.

Regards.

Posted 30-Nov-16 20:15pm

jamuro77

Comments

Faran Saleem 1-Dec-16 6:25am

Thanks a ton for your help.. i ran your query and it worked great just a couple of issues.

1. The difference between dates is coming in negetive.
2. And how can I select the records with difference between date < 7

Looking forward to your reply

Faran Saleem 1-Dec-16 6:48am

And in above example we are subtracting from the max date.. what if i want results only with 7 days difference. Like for suppose if we have 4 following dates
2016-03-02
2016-03-04
2016-03-06
2016-06-08

In above case 2016-06-08 is the max date but the difference between other 3 dates is in between 7 days.
So i want to display only those 3 dates and not 2016-06-08