基于数据分组的特定mysql更新

Question

这个让我难过.

我有2个表格如下:

METERS
id | startTime

READINGS
id | meter_id | readingTime

我想要做的是更新1 sql查询中meters.startTime的最低匹配readings.readingTime.

我该怎么做呢？

Answer 1

像这样:

UPDATE Meters m
INNER JOIN
(
   SELECT meter_id, MIN(reading_time) lowesttime
   FROM readings 
   GROUP BY meter_id
) r ON m.id = r.meter_id
SET m.starttime = r.lowesttime;