Postgresql Run Upsert function for Each record in Query

Question

I came across an example of UPSERT in postgresql manual here and I implemented it such that it works perfectly when I call the function and pass the arguments select myfunction(arg1,arg2,arg3). Now my problem is that I want to run a query that will select a number of records and insert/update a table using myfunction. The issue is how to pass each result from my select statement to the function as variables. I should probably use triggers but am lost as to where to start from. I hope you guys understand me. ofcourse if there is an entirely different and better way to go about this am all ears. Help pls

Answer 1

select myfunction(arg1,arg2,arg3)
  from (
    select arg1, arg2, arg3
      from data_table
      where something='something-other'
  ) as _;