SQL Queries with date comparison

Hello, I´m new to LN and want to make a SQL Query from "Application Customization" to display all Sales Positions with Planned Delivery witih the next 30 days.
The code in the Text-Editor:
select
tdsls401.orno | VK-Auftrag
from
tdsls401 | VK-Auftragspositionen
where
tdsls401.ddta > utc.num()
and tdsls401.ddta < date.to.utc(2020,12,20,0,0,0) | this works
| and tdsls401.ddta < date.to.utc(num.to.date(date.num()+30)) this says that no data can be selected

Can anybody help me?

Thanks, Martin