How to determine the auto-generated primary key used as a foreign key for another table

Question

This is a two-part question. Attached is a diagram for a PostgreSQL database table design. There are four tables. Table Main has a one-to-many relationship wi

Answer 1

Answer to Q1: Use data-modifying CTEs and return the serial PK with the RETURNING clause:

WITH ins_main AS (
   INSERT INTO main(col1)
   VALUES ('some value 1')
   RETURNING main_id    
   )
, ins_submain AS (
   INSERT INTO submain (main_id, col2)
   SELECT main_id, 'some value 2'
   FROM   ins_main
   RETURNING submain_id
   )
INSERT INTO subsub (submain_id, col3)
SELECT submain_id, 'some value 3'
FROM   ins_submain;

Requires Postgres 9.1 or later.
Related answers with explanation and links:

• Insert data in 3 tables at a time using Postgres
• PostgreSQL store value returned by RETURNING