此sql代码适用于应用于图1中的表：

SELECT
  t1.ID,
  t1.Module,
  t1.MoudleStatus,
  t1.UpdatedOn,
  IFNULL(DATEDIFF(
    t1.UpdatedOn,
    (SELECT MAX(t2.UpdatedOn) FROM ModuleFlowModuleStatus AS t2 WHERE t2.id < t1.id)
  ), 0) AS `Diff(Days)`
FROM
  ModuleFlowModuleStatus AS t1;

代码可以优化/改进一点，但对我来说很有用。为了简化代码，我省略了where和order by子句，您只需再次添加它们。如果有用请告诉我。哦，mysql datediff函数默认返回以天为单位的值，我认为这正是您想要的。

另一种方法是分配行号并联接

SELECT T.*, S.RN1,S.UPDATEDON,
         DATEDIFF(t.UPDATEDON,s.UPDATEDON) DIFF
FROM
(
SELECT T.*, 
         IF(T.MODULE <> @P , @RN:=1,@RN:=@RN+1) RN,
         @P:=T.MODULE P
FROM T
CROSS JOIN (SELECT @RN:=0,@P:='') R
where t.Module = 'LW2205'
order by t.module, t.id
)T 
LEFT JOIN
( 
SELECT T.*, 
         IF(T.MODULE <> @P1 , @RN1:=1,@RN1:=@RN1+1) RN1,
         @P1:=T.MODULE P1
FROM T
CROSS JOIN (SELECT @RN1:=0,@P1:='') R
where t.Module = 'LW2205'
order by t.module, t.id
) S
ON S.RN1 = T.RN - 1 AND S.MODULE = T.MODULE;

结果

+------+--------+-------------------------+---------------------+------+--------+------+---------------------+------+
| ID   | Module | MoudleStatus            | UpdatedOn           | RN   | P      | RN1  | UPDATEDON           | DIFF |
+------+--------+-------------------------+---------------------+------+--------+------+---------------------+------+
|    4 | LW2205 | Draft exam received     | 2017-10-18 12:41:12 |    1 | LW2205 | NULL | NULL                | NULL |
|    5 | LW2205 | Draft exam received     | 2017-10-18 12:41:23 |    2 | LW2205 |    1 | 2017-10-18 12:41:12 |    0 |
|    7 | LW2205 | Draft exam received     | 2017-10-20 15:06:46 |    3 | LW2205 |    2 | 2017-10-18 12:41:23 |    2 |
|  275 | LW2205 | Exam approved by Dean   | 2017-11-14 16:39:28 |    4 | LW2205 |    3 | 2017-10-20 15:06:46 |   25 |
|  288 | LW2205 | Final exam sign off by  | 2017-11-21 12:28:59 |    5 | LW2205 |    4 | 2017-11-14 16:39:28 |    7 |
|  295 | LW2205 | Exam sent to SREO (Stud | 2017-11-23 09:53:30 |    6 | LW2205 |    5 | 2017-11-21 12:28:59 |    2 |
+------+--------+-------------------------+---------------------+------+--------+------+---------------------+------+
6 rows in set (0.00 sec)

请注意，结果与预期结果不同