mysql - mysql中如何分组、排序和取出前N个？

Question

可以拿到组里排序好的数据，最后取出DolphinDB中的前N个。

但是在mysql中如何分组排序取出前N呢？

先谢谢你

DolphinDB代码如下:

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

Answer 1

如果你有支持 ROW_NUMBER() 的 MySQLv8.0，你可以使用这样的东西:

 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   

https://www.db-fiddle.com/f/8fY2DJmCCv7kCnEAPBAU3B/0