Postgres insert on conflict update using other table

Question

I having syntax error for the following sql which spent an hour but cant find any answer form postgres documentation.

CREATE TABLE transaction (userid SMALLINT, point INT, timestamp TIMESTAMPTZ);
CREATE TABLE point (userid SMALLINT PRIMARY KEY, balance1 INT, balance2 INT);
CREATE TABLE settings (userid SMALLINT, bonus INT);
INSERT INTO settings VALUES (1, 10); -- sample data

WITH trans AS (
  INSERT INTO transaction (userid, point, timestamp) 
  VALUES ($1, $2, NOW()) 
  RETURNING *
)
INSERT INTO point (userid, balance1) 
SELECT userid, point 
FROM trans -- first time
ON CONFLICT (userid) DO UPDATE 
  SET balance1=point.balance1 + excluded.balance1, 
      balance2=point.balance2 + excluded.balance1 + settings.bonus 
FROM settings -- tried USING, not work
WHERE settings.userid=excluded.userid;

My question is how can I include extra table without using FROM during update? My target is to keep all into 1 query.

user330315 · Accepted Answer · 2016-10-10 07:03:26Z

It's not totally clear to me what you are trying to do. The way I understand it, is that you are trying to use the value from settings.bonus when updating the row in case on conflict kicks in.

This can be done using a co-related sub-query in the UPDATE part:

WITH trans (userid, point, timestamp) AS (
  INSERT INTO transaction (userid, point, timestamp) 
  VALUES (1, 1, NOW()) 
  RETURNING *
)
INSERT INTO point (userid, balance1) 
SELECT trans.userid, trans.point 
FROM trans 
ON CONFLICT (userid) DO UPDATE 
  SET balance1 = point.balance1 + excluded.balance1, 
      balance2 = point.balance2 + excluded.balance1 + (select s.bonus 
                                                       from settings s 
                                                       where s.userid = excluded.userid)

Note however, that balance2 will never be incremented this way because on the first insert it will be null subsequent updates will try to add something to null but any expression involving null yields null (null + 5 is null).

So you either need to insert 0 when doing the insert the first time, or use coalesce() when doing the update, e.g.

balance2 = coalesce(point.balance2, 0) + excluded.balance1 + (select ...);

If it's possible that there is no row in settings for that user, then you need to apply coalesce() on the result of the sub-query as well:

... excluded.balance1 + coalesce( (select ... ), 0)

Also: you used excluded.point in your question which is incorrect. excluded refers to the target table point but that does not have a column point - you probably meant: excluded.balance1 (as that is the column into which the inserted trans.point will go)

^{Unrelated, but: timestamp is a horrible name for a column. For one because it's a keyword, but more importantly because it does not document what the column is for. Does it mean "created at"? "valid until"? "start at"? "obsolete from"? Something entirely different?}

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