Cannot SELECT from UPDATE RETURNING clause in postgres

Question

I isolatet the problem from a much more complex query. Here the test scenario

DROP TABLE test; 
CREATE TABLE test (
  id integer,
  description varchar(100)
         


        

Answer 1

Are you missing an IN: ... WHERE id IN (UPDATE ...?

However if I only run the statemennt "UPDATE test set value='test' RETURNING id", I get a result with 2 rows. Why is that?

Your UPDATE has no WHERE clause and therefore it updates every row, of which there are two.