-+---------+

你可以试试下面的方法，

DROP TABLE IF EXISTS groupTime ;
CREATE TABLE groupTime (
id INT(11) AUTO_INCREMENT PRIMARY KEY,
startFrom DATETIME(3),
endOn DATETIME(3),
gateway CHAR(1),
broadcast VARCHAR(8)
);

INSERT INTO groupTime (startFrom,endOn,gateway ,broadcast)
VALUES
('2018-09-01 23:41:24.024','2018-09-01 23:45:24.028','A','X01'),
('2018-09-01 23:41:24.025','2018-09-01 23:45:24.032','A','X01'),
('2018-09-01 23:41:24.026','2018-09-01 23:45:24.028','B','X01'),
('2018-09-01 23:41:24.030','2018-09-01 23:45:24.045','C','X01'),
('2018-09-01 23:41:24.029','2018-09-01 23:41:24.784','B','X02'),
('2018-09-01 23:41:24.025','2018-09-01 23:45:24.038','A','X01');

SELECT a.gateway, a.startfrom, a.endOn , TIMESTAMPDIFF(MICROSECOND , a.startfrom, a.endOn) FROM groupTime a 
INNER JOIN (
    SELECT MIN(id) AS id FROM groupTime WHERE broadcast='X01' GROUP BY gateway 
)AS b
ON a.id = b.id

演示

-+

试试这个：

select gateway, min(startFrom),min(endOn), TIMESTAMPDIFF(MICROSECOND, min(startFrom), min(endOn)) AS `timeDiff` 
from records
where broadcast = 'X01' GROUP BY gateway

-+---------+

-+

假设每个网关和广播都需要第一个，请使用以下命令：

select gateway, broadcast, timeDiff from (
    SELECT gateway, broadcast, TIMESTAMPDIFF(MICROSECOND, startFrom, endOn) AS timeDiff,
        row_number() over (partition by gateway, broadcast order by startfrom) as rn
    FROM Records ) q
where rn=1

编辑：看看mysql版本8 doc，语法是不同的

select gateway, broadcast, timeDiff from (
    SELECT gateway, broadcast, TIMESTAMPDIFF(MICROSECOND, startFrom, endOn) AS timeDiff,
        row_number() over w as rn
    FROM Records
    WINDOW w as (partition by gateway, broadcast order by startfrom)
) q
where rn=1