How do I do a deep copy with a single PostgreSQL query?

Question

I have three tables:

CREATE TABLE offers
(
  id serial NOT NULL PRIMARY KEY,
  title character varying(1000) NOT NULL DEFAULT ''::character varying
);

CREATE TABLE items
(
  id serial NOT NULL PRIMARY KEY,
  offer_id integer NOT NULL,
  title character varying(1000) NOT NULL DEFAULT ''::character varying,
  CONSTRAINT items_offer_id_fkey FOREIGN KEY (offer_id)
      REFERENCES offers (id) 
);

CREATE TABLE sizes
(
  id serial NOT NULL PRIMARY KEY,
  item_id integer NOT NULL,
  title character varying(1000) NOT NULL DEFAULT ''::character varying,
  CONSTRAINT sizes_item_id_fkey FOREIGN KEY (item_id)
      REFERENCES items (id) 
);

I have 1 offer that has 2 items. Each item has 2 sizes:

INSERT INTO offers (title) VALUES ('My Offer');
INSERT INTO items (offer_id, title) VALUES (1, 'First Item');
INSERT INTO items (offer_id, title) VALUES (1, 'Second Item');
INSERT INTO sizes (item_id, title) VALUES (1, 'First Size of Item #1');
INSERT INTO sizes (item_id, title) VALUES (1, 'Second Size of Item #1');
INSERT INTO sizes (item_id, title) VALUES (2, 'First Size of Item #2');
INSERT INTO sizes (item_id, title) VALUES (2, 'Second Size of Item #2');

Is there a way to clone an offer with all its items and sizes with a single query?

I tried to solve it with CTE, here is my SQL:

WITH tmp_offers AS (
    INSERT INTO offers (title)
    SELECT title FROM offers WHERE id = 1
    RETURNING id
), tmp_items AS (
    INSERT INTO items (offer_id, title)
    (SELECT (SELECT id FROM tmp_offers), title FROM items WHERE offer_id = 1)
    RETURNING id
)
INSERT INTO sizes (item_id, title)
(SELECT (SELECT id FROM tmp_items), title FROM sizes WHERE id IN (
    SELECT sizes.id FROM sizes
    JOIN items ON items.id = sizes.item_id
    WHERE items.offer_id = 1
));

But this SQL results to an error, that I can't resolve:

ERROR: more than one row returned by a subquery used as an expression

Your help is greatly appreciated.

PS I use PostgreSQL 9.5

Answer 1

This should work:

WITH tmp_offers AS (
    INSERT INTO offers (title)
    SELECT title 
    FROM offers 
    WHERE id = 1
    RETURNING id
), tmp_items AS (
    INSERT INTO items (offer_id, title)
    SELECT o.id, i.title 
    FROM items i
      cross join tmp_offers o
    WHERE i.offer_id = 1
    order by i.id
    RETURNING items.id
), numbered_new as (
  select ti.id, 
         row_number() over (order by ti.id) as rn
  from tmp_items ti
), numbered_old as (
  select i.id, 
         row_number() over (order by i.id) as rn
  from items i
  WHERE i.offer_id = 1
), item_mapper as (
  select n.id as new_item_id, 
         o.id as old_item_id
  from numbered_new n
     join numbered_old o on n.rn = o.rn
)
INSERT INTO sizes (item_id, title)
select im.new_item_id, s.title
from sizes s
  join item_mapper im on im.old_item_id = s.item_id;

Online example: http://rextester.com/RYQUS11008

Answer 2

You are quite close. It is the final query that needs work:

WITH tmp_offers AS (
      INSERT INTO offers (title)
          SELECT title FROM offers WHERE id = 1
          RETURNING id
     ),
    tmp_items AS (
     INSERT INTO items (offer_id, title)
        SELECT o.id, i.title
        FROM items i CROSS JOIN
             (SELECT id FROM tmp_offers) o
        WHERE i.offer_id = 1
        RETURNING id, title
)
INSERT INTO sizes (item_id, title)
    SELECT i.id, i.title
    FROM tmp_items i;

The major difference here is that tmp_items now has two columns -- and they appear to be the columns that you want for this purpose.