PostgreSQL IF value doesn't exist THEN INSERT value

Question

I've tried multiple variations of this code and it keeps giving me the SQL state: 42601 error. I've looked at the docs and tried using their examples which sometimes work, but do not do what I want.

IF (SELECT guildid FROM Servers <> 1) THEN
  INSERT INTO Servers (guildid) VALUES (1)
END IF;

My Servers table is simple. I just have a single row called guildid. I do not want a CASE statement because that only outputs messages.

Answer 1

If you don't have to worry about race conditions (which the if approach suggests), then:

INSERT INTO Servers (guildid)
   SELECT guildid
   FROM (VALUES (1)) v(guildid)
   WHERE NOT EXISTS (SELECT 1 FROM Servers s WHERE s.guildid = v.guildid);

To protect the table, I would suggest adding a unique index on it. In fact, just declare guildid to be the primary key. In that case, your original insert will simply fail, if you attempt to insert a duplicate value.

Answer 2

If you have a unique constraint on that column, you can use on conflict do nothing:

INSERT INTO Servers (guildid) VALUES (1)
ON CONFLICT DO NOTHING;