How to UPSERT (MERGE, INSERT … ON DUPLICATE UPDATE) in PostgreSQL?

Question

A very frequently asked question here is how to do an upsert, which is what MySQL calls INSERT ... ON DUPLICATE UPDATE and the standard supports as part of the

Answer 1

WITH UPD AS (UPDATE TEST_TABLE SET SOME_DATA = 'Joe' WHERE ID = 2 
RETURNING ID),
INS AS (SELECT '2', 'Joe' WHERE NOT EXISTS (SELECT * FROM UPD))
INSERT INTO TEST_TABLE(ID, SOME_DATA) SELECT * FROM INS

Tested on Postgresql 9.3