I am trying to save the results of a subquery into a table.

```
select (b.close - a.close) AS difference from day_ohlcs AS a inner join day_ohlcs AS b ON a.id + 1 = b.id

```

The speed of the subquery is fast, but when I try to put it in an update statement it takes forever, so I know I'm doing something wrong.

```
UPDATE day_ohlcs
SET price_change = t.difference
FROM (select (b.close - a.close) AS difference
    FROM day_ohlcs AS a 
    inner join day_ohlcs AS b 
    ON a.id + 1 = b.id) 
AS t
WHERE day_ohlcs.instrument_id = 1;

```

What am I not understanding? Thanks in advance.