Pentaho reporting with dropdown parameter

Pentaho reporting with dropdown parameter

I am creating a report with PDI as a datasource, now i need to use a drop
down parameter in my report. for that i have added a JDBC datasource and
wrote a SELECT sql that contains my dropdown list values and referred it
in my parameter. but when i publish my report it says 'the query is not
executable.' (If i change the parameter to a text box and my report works
fine)
I have tried using another transformation with the same sql as a table
input but the report still not opening and says 'Error -1'.
Report designer version: 3.6; Kettle version: 4.3;
How can i use a dropdown parameter when i use a PDI datasource?
Is it possible to add multiple datasources and use in a single report like
a PDI and JDBC?
or any other way to get a drop down parameter without bothering about
datasources?
I have googled and not able to find any solution.