Postgres insert coalesce?

Question

PostgreSQL

this query is not working

INSERT INTO 
  geo
(
  num_order
)
VALUES (
  COALESCE(max(num_order) + 1, 1)
);

although select COALESCE(max(num_order) + 1, 1) works fine

Answer 1

Use SELECT instead of VALUES:

INSERT INTO 
  geo
(
  num_order
)
SELECT  COALESCE(max(num_order) + 1, 1) from geo;

This code will work if there is at least one record in geo.