SQL Server: "All Values" option in Queried parameter

To add the option "All" in a Queried SQL parameter change your (list) dataset like this:

The dataset where you use the parameter should look something like this:

SELECT statecodename, statecode

FROM FilteredOpportunity AS CRMAF_FilteredOpportunity
WHERE (accountid = @CRM_Accountid) AND (statecode = @CRM_Opp_Statt) OR
(accountid = @CRM_Accountid) AND (@CRM_Opp_Statt = - 1)

For Text variables:
Use a (list) dataset, similar to this:

The dataset where you use the parameter should look something like this: