google cloud platform – GCP dataflow to PostgreSQL connectivity

We are trying to replace alteryx with GCP dataflow for ETL job. Requirement is to get data from PostgreSQL table, join, add some formulas and group by to add missing columns and then write back to PostgreSQL table again for Qlik to consume and generate Viz.
I am new to Java. Can anyone help me with any sample code to refer to for similar use case. That would be really helpful. Thank you

I am new to Java. Can anyone help me with any sample code to refer to for similar use case. Thank you