mysql - 跟踪当前和以前的状态

Question

我有一个表，它保存与 process_id 相对应的 status 和 created_timestamp。一旦进程状态发生变化，就会插入一行。因此，具有相同 process_id 的行的数量与与其相关联的状态的数量一样多。我想使用此数据创建另一个表/ View ，其中一行对应于一个process_id、它的当前状态和它以前的状态。我需要为此创建一个 Informatica 作业，但 SQL 查询也同样有用。
示例输入:

Process_id | Status     | Created 
         1 | In_queue   | 2014-08-01 00:01:01 
         1 | Started    | 2014-08-01 01:03:01 
         1 | In_process | 2014-08-01 01:50:20 
         1 | Complete   | 2014-08-01 03:10:20 

Sample Output: 
Process_id | Previous_status | Current_status | Updated 
         1 | In_process      | Complete       | 2014-08-01 03:10:20

Answer 1

SELECT Process_id, Previous_status, Current_status, Updated 
FROM (
    SELECT
    Process_id, 
    Status AS Current_status, 
    Created AS Updated,
    @prev_state AS Previous_status,
    @prev_state := Status 
    FROM
    your_table t
    , (select @prev_state := null) var_init
    WHERE Process_id = 1
    ORDER BY Created
) sq

更新:

要为所有 Process_id 执行此操作并仅获取每个 Process_id 的最新记录，您可以使用此方法:

SELECT sq.Process_id, sq.Previous_status, sq.Current_status, sq.Updated 
FROM (
    SELECT
    Process_id, 
    Status AS Current_status, 
    Created AS Updated,
    @prev_state := if(@prev_process != Process_id, null, @prev_state),
    @prev_state AS Previous_status,
    @prev_state := Status,
    @prev_process := Process_id
    FROM
    your_table t
    , (select @prev_state := null, @prev_process := null) var_init
    ORDER BY Process_id, Created
) sq
INNER JOIN (
    SELECT Process_id, MAX(Created) AS max_created
    FROM your_table
    GROUP BY Process_id
) max_c
ON sq.Process_id = max_c.Process_id AND sq.Updated = max_c.max_created