Days between two dates columns in DirectQuery

[ricgin]

 Hello community, 

I tried, unsuccesfuly, to subtract two date in DirectQuery but impossible.. 

How can I do this?

[NRB_UK]

I have been able to get this working by using the DATEVALUE DAX command.  This seems to reconfirm that these are Date fields.

Please check the results you get as the first time I tried this the results worked on 90% of the calculations.  Had to refresh to ensure all values were correct.

Example :

DATEVALUE(Table_Name[Date_Field_One]) - DATEVALUE(Table_Name[Date_Field_Two])

The returning field can then be formatted as required.

[Mi2n]

You might have to enable "Allow unrestricted measures in DirectQuery mode" from File -> Options and Settings -> Options -> DirectQuery, in order to use the DATEDIFF() function in order to subtract two dates.

But, beware, this will not restrict any potentially costly queries if you try to use them.

[ricgin]

Thanks, but I have an error message.. DATEDIFF() is not supported in DirectQuery mode.. 

Maybe avaible in the next release?

[pqian]

@ricgin, in the query editor, you should be able to substract two date columns by simply using the "-" operator. There's a ribbon operation for this: select the two columns, go to Add Column -> Time -> Substract.

The resultant column is of type Duration. When loaded into AS this will get converted to a bigint, which is accurate to 0.1ms. Then you can use simple math to extract the portion of this field. For example, to get to the total number of days:

Column = [TimeDifference] / 1E7 / 60 / 60 / 24

[Anonymous]

I get the same result via this method. 

  ! This step results in a query that is not supported in DirectQuery mode.

[ricgin]

Thanks, but doesn't work in DirectQuery mode..

[pqian]

@ricgin Given that the operation folds to SQL, it should work just fine in DQ mode.

What errors are you getting if you try this? What's the formula in the formula after the substraction?

[ricgin]

when I create a new column (in the query editor) to substract 2 columns, PowerBI Desktop said that : if I want to apply the changes I need to switch to import mode

[Anonymous]

Me too! 

[pqian]

It's actually quite interesting to note the way PowerQuery does this substraction...

select ...,
    convert(bigint, 
    (
        select convert(bigint, convert(bigint, datediff("ns", dateadd("ms", datediff("ms", dateadd("d", datediff("d", convert(datetime2, '0001-01-01 00:00:00'), [_].[StartDate]), convert(datetime2, '0001-01-01 00:00:00')), [_].[StartDate]), dateadd("d", datediff("d", convert(datetime2, '0001-01-01 00:00:00'), [_].[StartDate]), convert(datetime2, '0001-01-01 00:00:00'))), [_].[StartDate])) / 100) + (convert(bigint, datediff("ms", dateadd("d", datediff("d", convert(datetime2, '0001-01-01 00:00:00'), [_].[StartDate]), convert(datetime2, '0001-01-01 00:00:00')), [_].[StartDate])) * 10000 + convert(bigint, datediff("d", convert(datetime2, '0001-01-01 00:00:00'), [_].[StartDate])) * 864000000000) as [$Item]
    ) - 
    (
        select convert(bigint, convert(bigint, datediff("ns", dateadd("ms", datediff("ms", dateadd("d", datediff("d", convert(datetime2, '0001-01-01 00:00:00'), [_].[EndDate]), convert(datetime2, '0001-01-01 00:00:00')), [_].[EndDate]), dateadd("d", datediff("d", convert(datetime2, '0001-01-01 00:00:00'), [_].[EndDate]), convert(datetime2, '0001-01-01 00:00:00'))), [_].[EndDate])) / 100) + (convert(bigint, datediff("ms", dateadd("d", datediff("d", convert(datetime2, '0001-01-01 00:00:00'), [_].[EndDate]), convert(datetime2, '0001-01-01 00:00:00')), [_].[EndDate])) * 10000 + convert(bigint, datediff("d", convert(datetime2, '0001-01-01 00:00:00'), [_].[EndDate])) * 864000000000) as [$Item]
    )) as [TimeDifference]