INSERT rows into multiple tables in a single query, selecting from an involved table

Question

I have two tables of the following form (i.e., every foo is linked to exactly one bar).

CREATE TABLE foo (
    id INTEGER PRIMARY KEY,
    x INTEGER NOT NULL         


        

Answer 1

if id of bar is serial and have default value nextval('bar_id_seq'::regclass) you can manually call this function to get new ids in cte

with
s_bar as (
  SELECT id, z, nextval('bar_id_seq'::regclass) new_id
  FROM   bar
  WHERE  ...
),
s_foo as (
  SELECT x, y, bar_id
  FROM   foo
  WHERE  ...
),
i_bar as (
  INSERT INTO bar (id, z)
  SELECT new_id, z
  FROM   s_bar
),
i_foo as (
  INSERT INTO foo (x, y, bar_id)
  SELECT f.x, f.y, b.new_id
  FROM   s_foo f
  JOIN   s_bar b on b.id = f.bar_id
)
SELECT 1