Running a custom SQL in AWS Quicksight using PostgreSQL as a data source

Question

I am trying to run a custom query to visualize in Quicksight. I have tested my query using JetBrain's DataGrip, but failed to return the result in Quicksight. I, then, realized that some SQL functions cause error in Quicksight.

I have run these functions below one by one in Quicksight and got the following error.

select current_date;
select to_date('2020-10-10', 'yyyy-MM-dd');
select now();
select now() + '-1 day';

Error: Failed to Prepare Data Set QuickSight could not generate any output column after applying transformation. Check transform(s) and try again.

I have found one similar question here, but that didn't help me. How can I run these functions in Quicksight when the data source is PostgreSQL?