Days between orderdates per Customer and first order value - powerbi

Question

I am new to DAX and have 2 questions I would like answered for a project. I am working on figuring out what the first value per customer is so what amount does the customer come in with.
In addition I would like to know what is the time between customer's orders does the customer come back to buy something after a day, week or only after a year. And if a customer comes 5 times what is the time between the orders each time.
Data set
enter image description here
Now I tried the following but then I only get the first date back each time but then each customer gets the very first order date that exists.
First Order = CALCULATE(FIRSTDATE(Text[Datum].[Date]),VALUES(Text[Datum].[Date]))
How can I solve this two question with DAX

Answer 1

You can try the following:
Initial value for customer measure
Initial value =
-- find customers first appearance date
VAR first_date =
CALCULATETABLE (
FIRSTDATE ( 'Table'[Date] ),
-- remove all filters on 'Table'[Date]
REMOVEFILTERS ( 'Table'[Date] )
)
RETURN
CALCULATE (
SUM ( 'Table'[Value] ),
first_date
)
First order date measure
First Order =
CALCULATE (
FIRSTDATE ( 'Table'[Date] ),
REMOVEFILTERS ( 'Table'[Date] )
)
Days passed since last visit measure
Days passed =
VAR last_visit =
CALCULATE (
MAX ( 'Table'[Date] ),
'Table'[Date]
-- from example expecting Customer ID & Date form unique combination,
-- otherwise use MAX() instead
< SELECTEDVALUE ( 'Table'[Date] )
)
RETURN
DATEDIFF (
last_visit,
-- same here as above with SELECTEDVALUE()
SELECTEDVALUE ( 'Table'[Date] ),
DAY
)
The result will then look like this (represented in a table visual):