How to get multiple parallel periods set? - sql-server

Question

I would like to create a MDX query which returns a measure value for 15th day of each month between two dates.
For example, the result for 2010-01-01 and 2016-12-15 should be as below:
2016-12-15: 123
2016-11-15: 789
2016-10-15: 556
(...)
2010-01-15: 456
I know I can calculate the number of months between two dates using DateDiff() function. Also, I can use ParallelPeriod() function to get the value for the previous month.
However I have no idea how I can use these values together and "iterate" from 1 to DateDiff() result to create multiple ParallelPeriod() calls in the "Days" set.
WITH
MEMBER NumberOfMonths AS
DateDiff("m",
[Calendar].[Day].&[20100101].MemberValue,
[Calendar].[Day].&[20160315].MemberValue
)
SET Days AS {
PARALLELPERIOD([Calendar].[Month], 1, [Calendar].[Day].&[20160315]),
PARALLELPERIOD([Calendar].[Month], 2, [Calendar].[Day].&[20160315]),
PARALLELPERIOD([Calendar].[Month], 3, [Calendar].[Day].&[20160315])
-- (...) How to generate this set automatically, using NumberOfMonths?
}
SELECT
{ Days } ON 0,
{ Quantity } ON 1
FROM [MyCube]
Any help would be appreciated.

Answer 1

It's an interesting problem, and though there is a solution, reading the MDX reference just led me down blind alleys.
Here's how you can get a set of the fifteenth day of each month:
WITH SET Months
AS
[Calendar].[Month].Members
SET FifteenthDays AS
GENERATE(
Months,
StrToSet('HEAD(DESCENDANTS(Months.Current,[Calendar].[Day]),1).Item(0).Lead(14)')
)
SELECT {} ON 0,
FifteenthDays ON 1
FROM TheCube
You can adjust this to suit your requirements, by filtering the initial named set "Months" using your date parameters.
Here's what's going on:
The GENERATE/StrToSet combination applies the MDX inside the quotes to each member of the first set ("Months")
The Current function is like CurrentMember, but applied to a set within Generate() brackets.
The DESCENDANTS function gets all the month's "children" at the Day level (I had to use this rather than .Children as in my cube there's an additional generation - Weeks - between Months and Days)
The HEAD function gets the first day in the month. (If your Time dimension leaf level is not sorted in date order, you may need to wrap the set in an ORDER function).
MDX doesn't automatically figure out that a singleton set (HEAD({},1) will trivially always return a singleton or the empty set) is a member, and you can apply member functions on it. So before applying Lead, I have to use the Item() function. I don't know why this function works, because according to the documentation it has a different purpose.
Lead(14) gives you the 15th day of the month, because the argument is 0-based.

Answer 2

The MDX approach №1 (a calculated member with sum aggregation):
WITH
MEMBER [Measures].[Quantity15] AS
SUM(
[Calendar].[Day].[Day].Members,
IIF(
Right([Calendar].[Day].CurrentMember.Properties('Key'),2) = "15",
[Measures].[Quantity],
NULL
)
)
SELECT
NON EMPTY { [Calendar].[Day].&[20100101]:[Calendar].[Day].&[20160315] } ON 0,
{ [Measures].[Quantity15] } ON 1
FROM [MyCube]
The MDX approach №2 (without new members, filtering the set):
SELECT
NONEMPTY(
{[Calendar].[Day].&[20100101]:[Calendar].[Day].&[20160315]},
IIF(
Right([Calendar].[Day].CurrentMember.Properties('Key'),2) = "15",
1,
NULL
)
) ON 0,
{ [Measures].[Quantity] } ON 1
FROM [MyCube]