I can get the sorted data in the group, and finally take out the first N in DolphinDB.
But how do I group, sort and take out the first N in mysql?
Thank you first.
The DolphinDB code is as follows：
sym = `C`MS`MS`MS`IBM`IBM`C`C`C$symbol;
price= 49.6 29.46 29.52 30.02 174.97 175.23 50.76 50.32 51.29;
qty = 2200 1900 2100 3200 6800 5400 1300 2500 8800;
timestamp = [09:34:07,09:36:42,09:36:51,09:36:59,09:32:47,09:35:26,09:34:16,09:34:26,09:38:12];
t1 = table(timestamp, sym, qty, price);
select top 2 * from t1 context by sym csort timestamp;
timestamp sym qty price
--------- --- ---- ------
09:34:07 C 2200 49.6
09:34:16 C 1300 50.76
09:32:47 IBM 6800 174.97
09:35:26 IBM 5400 175.23
09:36:42 MS 1900 29.46
09:36:51 MS 2100 29.52
If you have MySQLv8.0 that supports ROW_NUMBER() you can use something like this:
SELECT `timestamp`,sym,qty,price
FROM
(
SELECT
`timestamp`,sym,qty,price,ROW_NUMBER() OVER (PARTITION BY sym ORDER BY timestamp ASC) AS ranking
FROM `table`
) t
WHERE ranking<3