PostgreSQL：CREATE FUNCTION 按主键返回一行

Question

I wrote the following function:

-- Authenticate: Get session_id with user_id
CREATE OR REPLACE FUNCTION sessions_get(bigint) RETURNS SETOF char(32) AS
$$
    SELECT strip_hyphens(id) as id FROM sessions WHERE user_id = $1;
$$
LANGUAGE SQL;

1. I want to be able to run the query SELECT sessions_get(1) to get the session ID with user ID 1. And, I want the name of the column returned to be id .

   Is that possible? Or, would the query have to be SELECT * FROM sessions_get(1) ? In that case, it'd be shorter to just write SELECT sessions_get(1) as id . Which is better?

2. Can I remove SETOF since I know this function will always return 0 or 1 rows? I know this because user_id is the primary key of the sessions table.

Answer 1

1. Change the function to:

    -- Authenticate: Get session_id with user_id CREATE FUNCTION sessions_get(bigint, OUT id char(32)) RETURNS SETOF char(32) AS $$ SELECT strip_hyphens(id) FROM sessions WHERE user_id = $1; $$ LANGUAGE SQL;

   Then, use the query: SELECT * FROM sessions_get(1) .

2. Use SETOF so that 0 rows are returned when none exist. Otherwise, you'll get 1 empty row.

Answer 2

To avoid returning SETOF you can always do this:

CREATE OR REPLACE FUNCTION sessions_get(IN a bigint, OUT id char(32)) RETURNS char(32) AS
$$
    SELECT strip_hyphens(id) INTO id FROM sessions WHERE user_id = $1;
    RETURN;
$$
LANGUAGE SQL;

Hope it helps.