MySQL：Select 多列，但每个不同值的最新值为一列

Question

I would like to select several colums. In one column there are two distinct values "top" and "bot". Every row has a timestamp. I would like to make sure, that for each value "top" and "bot" I do get the latest timestamp entry.

Table:

uid | datetime           | device | temp | hum
================================================
1   |2022-08-30 17:34:34 |top     |11.5  |88.90
2   |2022-08-30 17:34:22 |bot     |13.2  |88.90
3   |2020-10-06 13:48:33 |top     |24.3  |75.00
4   |2020-10-06 14:35:37 |bot     |21.7  |75.00

I would like to get the following result with the SQL statement:

datetime            | device | temp | hum
===========================================
2022-08-30 17:34:34 |top     |11.5  |88.90
2022-08-30 17:34:22 |bot     |13.2  |88.90

But what I get with my current statement is:

datetime            | device | temp | hum
===========================================
2020-10-06 13:48:33 |top     |24.3  |75.00
2020-10-06 14:35:37 |bot     |21.7  |75.00

So it's not the most current row, it is the oldest one.

My best SQL try so far is:

SELECT datetime, device, temp, hum 
FROM <table_name> 
WHERE uid=123456789 
GROUP BY device 
ORDER BY datetime DESC 
LIMIT 2

Answer 1

This one should work fine for you:

SELECT device, datetime 
FROM table_name 
WHERE datetime in (SELECT MAX(datetime) FROM table_name GROUP BY device)