CASE statement in Report Studio filters

Question

I wrote the following CASE statement in a Report Studio filter (Cognos 8 running on DB2):

CASE
    WHEN (
        _WEEK_OF_YEAR(?paramDate?) > _WEEK_OF_YEAR(_ADD_MONTHS(?paramDate?; -3))
    )
    THEN (
        [BusinessView].[QueryItem].[Week] <= _WEEK_OF_YEAR(?paramDate?)
        AND [BusinessView].[QueryItem].[Week] >= _WEEK_OF_YEAR(_ADD_MONTHS(?paramDate?; -3))
        AND [BusinessView].[QueryItem].[Year] = _YEAR(?paramDate?)
    )
    ELSE (
        ([BusinessView].[QueryItem].[Week] <= _WEEK_OF_YEAR(?paramDate?)
            AND [BusinessView].[QueryItem].[Year] = _YEAR(?paramDate?))
        OR ([BusinessView].[QueryItem].[Week] >= _WEEK_OF_YEAR(_ADD_MONTHS(?paramDate?; -3))
            AND [BusinessView].[QueryItem].[Year] = _YEAR(_ADD_MONTHS(?paramDate?; -3)))
    )
END

But I get the error XQE-PLN-0312: Filter expressions must evaluate to Boolean . Notice that the expressions under both WHEN and THEN and ELSE all do evaluate to boolean. Also, such expressions all work when put individually in a filter. So I argue the problem is about the CASE statement itself. Also notice that I wrote other CASE filters in other reports and they work as I expect. Hence I suspect some trouble with date functions interacting with CASE .

I found out this answer, but it didn't fix the problem: as you can see in my code I already put all the parentheses in place.

Please don't suggest me to avoid the CASE statement and use instead AND and OR alone; this actually works, but I would like to understand how to make the CASE working as well.

Answer 1

There is no need any [if] or [case] statement. Just write filter conditions with logical operators.

Answer 2

Your CASE statement is invalid. All paths of a CASE statement must return a value. Try running your result expressions independently of the CASE statement. For example...

[BusinessView].[QueryItem].[Week] <= _WEEK_OF_YEAR(?paramDate?)
AND [BusinessView].[QueryItem].[Week] >= _WEEK_OF_YEAR(_ADD_MONTHS(?paramDate?; -3))
AND [BusinessView].[QueryItem].[Year] = _YEAR(?paramDate?)

...will result in an error.

Also, "The data types of else_result_expression and any result_expression must be the same or must be an implicit conversion." ( https://docs.microsoft.com/en-us/sql/t-sql/language-elements/case-transact-sql?view=sql-server-2017 )

The result of a filter must be either true or false.

So something like this?

CASE
  WHEN A=B
    THEN 'value1'
  WHEN A=C
    THEN 'value2'
  ELSE 'value3'
END = 'value3'