Write a Postgres Get or Create SQL Query

Question

I want to write a single Postgres SQL statement that says look for a user with color X and brightness Y. If that user exists, return all of its row data. If not, create a new

Answer 1

Adding my solution here. It is a tad different than @Clodoaldo Neto and @astef's solutions.

WITH ins AS (
  INSERT INTO mytable (color, brightness, size, age)
  VALUES ('X', 'Y', 'big', 'old')
  ON CONFLICT (color) DO NOTHING
  RETURNING *
)
SELECT * FROM ins
UNION
SELECT * FROM mytable
  WHERE color = 'X';

I found astef's solution inadequate for my purposes: it doesn't perform the "get" portion of "get or create"! If the value already existed, nothing would happen.

The union at the end of the statement ensures that if the value was not inserted (since it already existed) we still retrieve that value from the table.