Create a SQLite view where a row depends on the previous row

Question

I'd like to create a view in SQLite where a field in one row depends on the value of a field in the previous row. I could do this in Oracle using the LAG analytic function, but not sure how to go about it in SQLite.

For example, if my table looked like:

ITEM        DAY           PRICE
apple       2011-01-07    1.25
orange      2011-01-02    1.00
apple       2011-01-01    1.00
orange      2011-01-03    2.00
apple       2011-01-08    1.00
apple       2011-01-10    1.50

I'd like my view to look like, with WHERE item = 'apple':

DAY           PRICE    CHANGE
2011-01-01    1.00     (null)
2011-01-07    1.25     0.25
2011-01-08    2.00     0.75
2011-01-10    1.50     -0.50

Edit:

The equivalent of the query I'm looking for would look in Oracle something like (haven't tried this, but I think this is correct):

SELECT day, price, 
       price - LAG( price, 1 ) OVER ( ORDER BY day ) AS change
  FROM mytable
 WHERE item = 'apple'

Answer 1

Oracle equivalent is correct. Starting from SQLite 3.25.0 you could use LAG natively:

WITH mytable(ITEM,DAY,PRICE) AS (
    VALUES
    ('apple',  CAST('20110107' AS DATE),    1.25),
    ('orange', CAST('20110102' AS DATE),    1.00),
    ('apple',  CAST('20110101' AS DATE),    1.00),
    ('orange', CAST('20110103' AS DATE),    2.00),
    ('apple',  CAST('20110108' AS DATE),    2.00),
    ('apple',  CAST('20110110' AS DATE),    1.50)
)
SELECT day, price, price-LAG(price) OVER (ORDER BY day) AS change
FROM mytable
WHERE item = 'apple'
ORDER BY DAY;

db<>fiddle demo

Answer 2

Its the same idea as the other, but just uses the fields instead of the rowid. This does exactly what you want:

CREATE TABLE Prices (
    day DATE,
    price FLOAT
);

INSERT INTO Prices(day, price) VALUES(date('now', 'localtime', '+1 day'), 0.5);
INSERT INTO Prices(day, price) VALUES(date('now', 'localtime', '+0 day'), 1);
INSERT INTO Prices(day, price) VALUES(date('now', 'localtime', '-1 day'), 2);
INSERT INTO Prices(day, price) VALUES(date('now', 'localtime', '-2 day'), 7);
INSERT INTO Prices(day, price) VALUES(date('now', 'localtime', '-3 day'), 8);
INSERT INTO Prices(day, price) VALUES(date('now', 'localtime', '-4 day'), 10);

SELECT p1.day, p1.price, p1.price-p2.price 
FROM
    Prices p1, Prices p2,
    (SELECT t2.day AS day1, MAX(t1.day) AS day2 
    FROM Prices t1, Prices t2
    WHERE t1.day < t2.day
    GROUP BY t2.day) AS prev
WHERE p1.day=prev.day1
    AND p2.day=prev.day2

If you want to add the WHERE item='apple' bit you'd add that to both WHERE clauses.