postgres returning id, insert or select if id is present or not

问题

WITH x AS (
   INSERT INTO users(name, age)
    SELECT 'john', 30
    WHERE NOT EXISTS (
       SELECT id FROM users WHERE name = 'john' 
    ) u
    RETURNING (CASE WHEN u.id > 0 THEN u.id ELSE id END)
)

SELECT * FROM x

How can I always return an id and if the id is not present, then insert it. Also, I need this to be in a CTE.

来源：https://stackoverflow.com/questions/24050779/postgres-returning-id-insert-or-select-if-id-is-present-or-not