QE-DEF-0405 Incompatible data types in case statement. Very urgent

[rama83]

Hi All,

I am creating the report in Cognos 8.2 Report Studio.

Here i crated prompts on Year,Qtr,Month and Day.Here year-Number,Qtr-Char,Month-char and Day -date&time data types.And also i created one parameter for user selection
suppose in prompt page he select year he can see the year wise data............
Ex:-I created following Query item
Case Time_period
when ('year')     then (year)
when ('qtr')       then (quarter)
when ('month')  then (month)
when ('day')      then (day)
else (null)
end

When validating the query item i getting following error

QE-DEF-0459 CCLException
QE-DEF-0405 Incompatible data types in case statement.

Please any one give the solution its very useful for me
Thanks in advance

Regards,
Rama