我试图在一个有500,000条记录和50或60列的表中创建一个查询.我需要的是将这些记录整理成组并选择每组中的最大记录.
为了简化问题,我有一个表格如下
+----+-------------+----------+--------+
| id | external_id | group_id | mypath |
+----+-------------+----------+--------+
| 1 | 1003 | 1 | a |
| 2 | 1004 | 2 | b |
| 3 | 1005 | 2 | c |
+----+-------------+----------+--------+
简单组如下
select * from temp GROUP BY group_id
返回
+----+-------------+----------+--------+
| id | external_id | group_id | mypath |
+----+-------------+----------+--------+
| 1 | 1003 | 1 | a |
| 2 | 1004 | 2 | b |
+----+-------------+----------+--------+ …