通过MYSQL中的两个不同列对行进行分组

Question

我只想问是否可以对具有相同值但来自不同列的行进行分组。

我有一种情况，如果发现记录为“连续”交易，我们应该通过检查 STARTDATETIME 列是否与以前的数据 ENDDATETIME 相匹配来汇总总分钟数列是否相同。请参阅下面的图像链接以供参考。

谢谢大家。

Answer 1

我修改了戈登·利诺夫（Gordon Linoff）的solution（请参阅问题下方的评论）：

SELECT 
  c.employee_id
  ,MIN(c.start_date) AS start_date
  ,MAX(c.end_date) AS end_date
  ,COUNT(*) AS numcontracts,
  TIMESTAMPDIFF(minute,MIN(c.start_date),MAX(c.end_date)) AS timediff
FROM 
  (
    SELECT 
    c0.*
    ,(@rn := @rn + COALESCE(startflag, 0)) AS cumestarts
    FROM 
    (SELECT c1.*,
             (NOT EXISTS (SELECT 1
                  FROM contracts c2
                  WHERE c1.employee_id = c2.employee_id AND
                    c1.start_date = c2.end_date
                 )
             ) AS startflag
          FROM contracts c1
          ORDER BY employee_id, start_date

    ) c0 CROSS JOIN (SELECT @rn := 0) params

  ) c
GROUP BY c.employee_id, c.cumestarts

http://rextester.com/VOGMU19779

timediff包含组合时间间隔中经过的分钟数。