SSAS Tabular DAX using of IF Statement - if-statement

Question

I have this query written in SQL:
SELECT
CustomerId,
CustomerType,
CASE WHEN CustomerStatus = 'VIP'
THEN CustomerDiscountType
ELSE NULL
END AS CustomerDiscountType
FROM Customer
And I would like to write this in DAX query:
I know that I can write like this:
EVALUATE
(
SUMMARIZE
(
'Customer',
'Customer'[CustomerId],
'Customer'[Type],
'Customer'[DiscountType],
"Customer VIP", IF('Customer'[Status] = "VIP", 'Customer'[DiscountType], BLANK())
)
)
But when I write if condition I need include attribute 'Customer'[DiscountType] in that query too, but I would like to write the column name of that IF statement
"DiscountType", but it isn't possible for me like below.
EVALUATE
(
SUMMARIZE
(
'Customer',
'Customer'[CustomerId],
'Customer'[Type],
"DiscountType", IF('Customer'[Status] = "VIP", 'Customer'[DiscountType], BLANK())
)
)
It failed with this error because of existing DiscountType column:
Function 'SUMMARIZE' cannot add column [DiscountType] since it already exists.

Answer 1

Instead of using SUMMARIZE you can use SELECTCOLUMNS function. I think the error is caused because the IF function returns DiscountType column and it already exists in your Customer table. Also I am unsure if SUMMARIZE works without any aggregation like used in your DAX expression.
Try this expression:
EVALUATE
(
SELECTCOLUMNS (
'Customer',
"CustomerId", 'Customer'[CustomerId],
"Type", 'Customer'[Type],
"DiscountType", IF ( 'Customer'[Status] = "VIP", 'Customer'[DiscountType], BLANK () )
)
)
UPDATE: OP tells via comments the version used is SSAS 2014 which doesn't support SELECTCOLUMNS function.
You can use a mix of SUMMARIZE and ADDCOLUMNS functions to get the expected result.
EVALUATE
(
SUMMARIZE (
ADDCOLUMNS (
ADDCOLUMNS (
DISTINCT ( Customer[CustomerID] ),
"Type", CALCULATE ( VALUES ( Customer[Type] ) ),
"Status", CALCULATE ( VALUES ( Customer[Status] ) ),
"DiscountType1", CALCULATE ( VALUES ( Customer[DiscountType] ) )
),
"DiscountType", IF ( [Status] = "VIP", [DiscountType1], BLANK () )
),
[CustomerId],
[Type],
[DiscountType]
)
)
It is not tested but should work, let me know if this helps for you.