Insert (if not present) and return id

问题

I have a unique column. I want to insert a row if it's not already there, and then return the id of that row.

INSERT INTO t(a) VALUES ('a') ON CONFLICT DO NOTHING RETURNING t.id;

returns nothing at all. Here's a fiddle.
I'm looking for how to get 1 each time, whether 'a' was newly inserted or not.

回答1:

with i as (
    INSERT INTO t(a) VALUES ('a') ON CONFLICT (a) DO NOTHING RETURNING id
)
select id from i
union all
select id from t where a = 'a'
limit 1

来源：https://stackoverflow.com/questions/46946313/insert-if-not-present-and-return-id