GROUP BY用于SQL中的连续行

Question

鉴于下表:

ID   State  Date
12   1      2009-07-16 10:00
45   2      2009-07-16 13:00
67   2      2009-07-16 14:40
77   1      2009-07-16 15:00
89   1      2009-07-16 15:30
99   1      2009-07-16 16:00

问题:
我如何通过"国家"字段进行GROUP,同时仍保持状态变化之间的边界？

SELECT MIN(ID) AS ID, State, MIN(Date) AS Date, COUNT(ID) AS Count
FROM table GROUP BY State

结果如下:

ID   State  Date              Count
12   1      2009-07-16 10:00  4
45   2      2009-07-16 13:00  2

但这是预期的:

ID   State  Date              Count
12   1      2009-07-16 10:00  1
45   2      2009-07-16 13:00  2
77   1      2009-07-16 15:00  3

这在SQL中可行吗？到目前为止我没有找到解决方案......

Answer 1

SELECT  MIN(id) AS id, MIN(ts) AS ts, MIN(state) AS state, COUNT(*) cnt
FROM    (
        SELECT  @r := @r + (@state != state) AS gn,
                @state := state AS sn,
                s.*
        FROM    (
                SELECT  @r := 0,
                        @state := 0
                ) vars,
                t_state s
        ORDER BY
                ts
        ) q
GROUP BY
        gn

用于测试的表创建脚本:

CREATE TABLE t_state (id INT NOT NULL PRIMARY KEY, state INT NOT NULL, ts DATETIME NOT NULL);

INSERT
INTO  t_state
VALUES
(12,   1,      '2009-07-16 10:00'),
(45,   2,      '2009-07-16 13:00'),
(67,   2,      '2009-07-16 14:40'),
(77,   1,      '2009-07-16 15:00'),
(89,   1,      '2009-07-16 15:30'),
(99,   1,      '2009-07-16 16:00');