Imagine multiple parent-child tables with 1:M relationships. I would like to "cascade"-insert duplicate rows based on root parent table row selection.Each table has IDENTITY
primary key and each child table has FK to its parent ID (one level up).
The goal
Given root parent table ID, insert duplicate rows for it and all of its children.
I tried "cascading"-insert CTEs, but ran into issues where RETURNING
is limited to return only inserted data, while I need extra information to connect the next INSERT
.
I was able to accomplish this by adding an extra column (copied_from_id
).
My question
Is there a way to accomplish the same without extra column?
I did see this answer by @Erwin Brandstetter but his example only has 1 parent and child and I was not sure how to extend this to multiple levels
Example
Here is example DDL and DML to illustrate the issue
- lvl_one - top most, root, parent table
- lvl_two - child table of lvl_one (1:M)
- lvl_three - child table of lvl_two (1:M)
Setup
--DROP TABLE IF EXISTS lvl_one,lvl_two,lvl_three CASCADE;CREATE TABLE IF NOT EXISTS public.lvl_one ( id bigint NOT NULL GENERATED ALWAYS AS IDENTITY, name text, CONSTRAINT lvl_one_pk PRIMARY KEY (id));CREATE TABLE IF NOT EXISTS public.lvl_two ( id bigint NOT NULL GENERATED ALWAYS AS IDENTITY, lvl_one_id bigint NOT NULL, name text, CONSTRAINT lvl_two_pk PRIMARY KEY (id), CONSTRAINT lvl_two_lvl_one_id_fk FOREIGN KEY (lvl_one_id) REFERENCES public.lvl_one (id) );CREATE TABLE IF NOT EXISTS public.lvl_three ( id bigint NOT NULL GENERATED ALWAYS AS IDENTITY, lvl_two_id bigint NOT NULL, name text, CONSTRAINT lvl_three_pk PRIMARY KEY (id), CONSTRAINT lvl_three_lvl_two_id_fk FOREIGN KEY (lvl_two_id) REFERENCES public.lvl_two (id) );
Initial data
-- initial dataINSERT INTO lvl_one(name) VALUES ('Honda'), ('Ford'), ('Toyota');INSERT INTO lvl_two(lvl_one_id, name) VALUES (1,'Civic'), (1,'Passport'), (3,'Prius');INSERT INTO lvl_three(lvl_two_id, name) VALUES (1,'door'), (1,'window'), (3,'trunk');SELECT * FROM lvl_one ORDER BY id;-- id, name-- 1, "Honda"-- 2. "Ford"-- 3, "Toyota"SELECT * FROM lvl_two ORDER BY id;-- id, lvl_one_id, name-- 1, 1, "Civic"-- 2, 1, "Passport"-- 3, 3, "Prius"SELECT * FROM lvl_three ORDER BY id;-- id, lvl_two_id, name-- 1, 1, "door"-- 2, 1, "window"-- 3, 3, "trunk"SELECT one.id AS one_id, one.name AS one_name, two.id AS two_id, two.name AS two_name, three.id AS three_id, three.name AS three_nameFROM lvl_one AS one LEFT OUTER JOIN lvl_two AS two ON one.id = two.lvl_one_idLEFT OUTER JOIN lvl_three AS three ON two.id = three.lvl_two_idORDER BY one.id, two.id, three.id;--1 "Honda" 1 "Civic" 1 "door"--1 "Honda" 1 "Civic" 2 "window"--1 "Honda" 2 "Passport" NULL NULL --2 "Ford" NULL NULL NULL NULL --3 "Toyota" 3 "Prius" 3 "trunk"
Solution (with adding extra column)
ALTER TABLE lvl_one ADD COLUMN copied_from_id bigint;ALTER TABLE lvl_two ADD COLUMN copied_from_id bigint;ALTER TABLE lvl_three ADD COLUMN copied_from_id bigint;-- copy row id=1 from lvl_one and all its child tablesWITH source_one AS ( SELECT id,name FROM lvl_one WHERE id=1), copy_one AS ( INSERT INTO lvl_one(name,copied_from_id) SELECT name,id AS copied_from_id FROM source_one RETURNING id AS new_one_id, copied_from_id), copy_two AS ( INSERT INTO lvl_two(lvl_one_id,name,copied_from_id) SELECT new_one_id, lvl_two.name,lvl_two.id AS copied_from_id FROM copy_one INNER JOIN lvl_one ON lvl_one.id = copy_one.copied_from_id INNER JOIN lvl_two ON lvl_two.lvl_one_id = lvl_one.id RETURNING id AS new_two_id, copied_from_id), copy_three AS ( INSERT INTO lvl_three(lvl_two_id,name,copied_from_id) SELECT new_two_id, lvl_three.name, lvl_three.id AS copied_from_id FROM copy_two INNER JOIN lvl_two ON lvl_two.id = copy_two.copied_from_id INNER JOIN lvl_three ON lvl_three.lvl_two_id = lvl_two.id RETURNING id AS new_three_id, copied_from_id)SELECT * FROM copy_one, copy_two, copy_three;
Expected results of duplicating lvl_one.id=1
Following rows will be created in all 3 tables as a result of "duplicating" lvl_one.id=1
row.
-- lvl_one-- 4,Honda,1-- lvl_two--4,4,Civic,1--5,4,Passport,2-- lvl_three--4,4,door,1--5,4,window,2