在mysql中查找最后一个序列的开始时间

Question

我有下表，其中状态 0 用于非活动设备，状态 1 用于活动设备。

CREATE TABLE `devices` (
  `id` int NOT NULL AUTO_INCREMENT,
  `state` int unsigned NOT NULL,
  `dt` datetime NOT NULL,
  `name` varchar(60) COLLATE utf8_unicode_ci DEFAULT NULL,
   PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

INSERT INTO devices (state,name,dt) VALUES (1,'Alfa','2021-10-12 11:30:00');
INSERT INTO devices (state,name,dt) VALUES (0,'Alfa','2021-10-12 11:40:00');
INSERT INTO devices (state,name,dt) VALUES (1,'Alfa','2021-10-12 11:50:00');
INSERT INTO devices (state,name,dt) VALUES (1,'Alfa','2021-10-12 12:00:00');

INSERT INTO devices (state,name,dt) VALUES (1,'Beta','2021-10-12 11:30:00');
INSERT INTO devices (state,name,dt) VALUES (0,'Beta','2021-10-12 11:40:00');
INSERT INTO devices (state,name,dt) VALUES (0,'Beta','2021-10-12 11:50:00');
INSERT INTO devices (state,name,dt) VALUES (0,'Beta','2021-10-12 12:00:00');

http://sqlfiddle.com/#!9/8ea07de/3

查询的预期结果是：

Name    State   FROM                    TO
Alfa    1       '2021-10-12 11:50:00'   '2021-10-12 12:00:00'
Beta    0       '2021-10-12 11:40:00'   '2021-10-12 12:00:00'

目前我只能获取“名称”、“到”和“状态”列。 是否可以为 MySQL 5.6 找到具有预期结果（“来自”列）的查询？

Answer 1

您可以使用下一个查询：

SET @state = -1; -- initial value not equal to real values
SET @dt = '';    -- initial value not equal to real dates

SELECT 
    name,
    state,
    from_dt,
    dt
FROM (
  -- get last dt by name
  SELECT name, max(dt) dt
  FROM devices
  GROUP BY name
) last_state
JOIN (
  SELECT 
    name,
    state,
    dt,
    -- store dt eachtime when state changes
    @dt := IF(@state <> state, dt, @dt) from_dt,
    @state := state
  FROM devices
  ORDER BY name, dt ASC
) first_state using (name, dt)
;

MySQL fiddle