Report Parameters - Decimal vs. Float

My dataset returns data from a range of effective dates for a single
month. In the database, these dates are unfortunately not of type
datetime, but are decimal and are in the YYYYMMDD format.
I'm having trouble getting the report to execute because at the query
level, the datatype has to be decimal. I need to parameterize these
dates, but there is no decimal datatype for parameters.
I have a dataset that generates the necessary dates based on the type
of report the user wants (60/90/120 day) (if they want a 60-day report,
the effective date = 2 months from the first day of the current month,
etc).
SELECT DISTINCT
CONVERT(datetime,LEFT(CAST(effdte AS varchar), 4) + '/' +
SUBSTRING(CAST(effdte AS varchar), 5, 2) + '/' + '01') +
@.period_additive AS effdte_low,
CONVERT(datetime,LEFT(CAST(effdte AS varchar), 4) + '/' +
SUBSTRING(CAST(effdte AS varchar), 5, 2) + '/' + '31') +
@.period_additive AS effdte_high
FROM dbo.t_policy
WHERE YEAR(GETDATE()) - 1 = LEFT(CAST(effdte AS varchar), 4) AND
MONTH(GETDATE()) = SUBSTRING(CAST(effdte AS varchar), 5, 2) AND
LEFT(policy, 3) LIKE @.dept_cd AND LEFT(policy, 3) <> 'LPA'
What would the appropriate code be to do this within the Report
Parameters dialog instead? It seems like I'd have a better chance of
success if it were done that way.
Thanks!
MikeNo matter what, I get this error at runtime (Preview mode):
--
Processing Errors
--
An error has occurred during report processing.
Cannot read the next data row for the data set ds_main.
Arithmetic overflow error converting expression to data type datetime.
--
OK
--|||I think I fixed it...
Even though the database type is decimal, when searching by that range,
I have to put single quotes around it. Therefore, I converted the date
type back to a varchar and changed the parameter data types to string.
Now the report runs.
But there should be a more straightforward way to do this within the
Report Parameters dialog box, shouldn't there?sql