Finding the difference between two values in the same column in MySQL
I have a simple table called that contains share prices in MySQL:
Table `share_prices`
+----------+-------+---------------------+
| stock_id | price | date |
+----------+-------+---------------------+
| 1 | 0.05 | 2010-02-24 01:00:00 |
| 2 | 3.25 | 2010-02-24 01:00:00 |
| 3 | 3.30 | 2010-02-24 01:00:00 |
| 1 | 0.50 | 2010-02-23 23:00:00 |
| 2 | 1.90 | 2010-02-23 23:00:00 |
| 3 | 2.10 | 2010-02-23 23:00:00 |
| 1 | 1.00 | 2010-02-23 19:00:00 |
| 2 | 1.00 | 2010-02-23 19:00:00 |
| 3 | 1.00 | 2010-02-23 19:00:00 |
+----------+-------+---------------------+
Every time a share price is updated, a new row is inserted into the table.
With this structure, how can I return a query that shows the price change in the last 24 hours?
The desired result would be:
+----------+开发者_开发百科------+------+------------+
| stock_id | then | now | difference |
+----------+------+------+------------+
| 3 | 1.00 | 3.30 | 2.30 |
| 2 | 1.00 | 3.25 | 2.25 |
| 1 | 1.00 | 0.05 | -0.95 |
+----------+------+------+------------+
What's the best way to go about this? Some kind of join? A sub-query?
What I think I'm aiming for is to essentially query once to get then
, query again to get now
and then somehow glue it all together at the end.
Edit: I need to account for negative changes too.
Ok, got home, and was able to figure this out.
SELECT stock_id, t1.price AS `then`, t2.price AS `now`, ROUND(t2.price - t1.price, 2) AS `difference`
FROM (
SELECT stock_id, price, date FROM share_prices sp
WHERE date = (SELECT MIN(date) FROM share_prices sp2
WHERE date BETWEEN '2010/02/23 10:00:00'
AND '2010/02/24 10:00:00'
AND sp2.stock_id = sp.stock_id)
) t1
JOIN
(
SELECT stock_id, price, date FROM share_prices sp
WHERE date = (SELECT MAX(date) FROM share_prices sp2
WHERE date BETWEEN '2010/02/23 10:00:00'
AND '2010/02/24 10:00:00'
AND sp2.stock_id = sp.stock_id)
) t2 USING(stock_id)
ORDER BY `difference` DESC
Uses the results from 2 subqueries, each with their own subquery to the first and last, respectively, record for that range.
I was using integer
for stock_id
, float
for price
and timestamp
for date, since there may be issues (notably with the MIN and MAX) with other data types.
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