SQL trigger function to UPDATE daily moving average upon INSERT

Question

I am trying to create a SQL trigger function which should UPDATE a column when data is INSERTed INTO the table. The update is based on the values present in the values being INS

Answer 1

Can't you just do something along those lines?

INSERT INTO daily_ohlc 
SELECT current_date, 101, 110, 95, 108, (COUNT(*)*AVG(close)+108)/(1+Count(*))
FROM daily_ohlc
WHERE cDate >= ANY (
    SELECT MIN(cdate)
    FROM (SELECT CDate, ROW_NUMBER() OVER (ORDER BY CDate DESC) as RowNum FROM daily_ohlc) a 
    WHERE RowNum <= 7
)

I know very well it could appear complicated compared to a trigger.
However, I am trying to avoid a case where you successfully create the ON INSERT trigger and next want to handle updates in the table. Updating a table within a procedure triggered by an update in the same table is not the best idea.

Answer 2

You may do an UPDATE FROM your select query using appropriate joins in your Trigger.

create or replace function update_sma8() RETURNS TRIGGER AS
$$
 BEGIN

UPDATE daily_ohlc d SET sma8 = s.simple_mov_avg 
FROM
(
 SELECT  sec.cdate,AVG(sec.close)  
   OVER(ORDER BY sec.cdate ROWS BETWEEN 7 PRECEDING AND CURRENT ROW) AS 
    simple_mov_avg FROM daily_ohlc sec
)s where s.cdate = NEW.cdate  --The newly inserted cdate
     AND d.cdate = s.cdate;   
RETURN NULL;

END $$ language plpgsql;

Demo

The only caveat of using this method is that if someone deletes a row or updates close column, then the values have to be recalculated, which won't happen for existing rows. Only the inserted row will see the right re-calculated value.

Instead, you may simply create View to calculate the sma8 column from the main table for all rows when requested.