Updatable view
Only simple views accept INSERT, UPDATE and DELETE. A view with GROUP BY has no single row to change. v_agg is such a view.
task
v_agg is an aggregate view. Try to insert into it and read the error.
Run a query to see rows here.
Run EXPLAIN on the statement under the cursor: Plan tab, button Explain.
No tables yet.
Only simple views accept INSERT, UPDATE and DELETE. A view with GROUP BY has no single row to change. v_agg is such a view.
v_agg is an aggregate view. Try to insert into it and read the error.