每个x字段只有n条记录

Question

鉴于此数据集：

ID  Name            City            Birthyear
1   Egon Spengler   New York        1957
2   Mac Taylor      New York        1955
3   Sarah Connor    New York        1959
4   Jean-Luc Picard La Barre        2305
5   Ellen Ripley    Nostromo        2092
6   James T. Kirk   Nostromo        2233
7   Henry Jones     La Barre    1899

如何从每个城市只获得2条记录？

Answer 1

试试这个：

SELECT i1.*
FROM your_table i1
LEFT JOIN your_table i2
  ON (i1.City = i2.City AND i1.ID > i2.ID)
GROUP BY i1.ID
HAVING COUNT(*) < 2
ORDER BY city, ID;