BIRT reporting

Any body has experiance using BIRT report ?
I have one report parameter.
I just want to create if the user specify the report parameter, the sql will
execute sql with where clause (ex: select * from user where userid=?), but
if no report parameter specify, i want to execute the sql without where
clause. (Ex: select * from user)
Is this possible ?

specify query in the Data Set's beforeOpen method, like


this.queryText = "SELECT * FROM " + params["myParam"]