Error when joining a table to itself - mysql

Question

I have a table where the data of measured temperature and humidity is stored. Records with temperature have the field meas_kind set to "T", and for humidity it is set to "H".
mysql> describe meteo;
+-----------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+----------------+
| id | bigint(20) unsigned | NO | PRI | NULL | auto_increment |
| meas_time | timestamp | YES | | NULL | |
| room | varchar(10) | NO | | NULL | |
| meas_kind | char(1) | NO | | NULL | |
| value | double | NO | | NULL | |
+-----------+---------------------+------+-----+---------+----------------+
mysql> select * from meteo;
+----+---------------------+------+-----------+-------+
| id | meas_time | room | meas_kind | value |
+----+---------------------+------+-----------+-------+
| 35 | 2017-05-24 16:51:47 | 123 | T | 22.61 |
| 36 | 2017-05-24 16:51:47 | 123 | H | 36.93 |
| 37 | 2017-05-24 16:51:51 | 123 | T | 22.61 |
| 38 | 2017-05-24 16:51:51 | 123 | H | 36.94 |
| 39 | 2017-05-24 16:51:56 | 123 | T | 22.61 |
| 40 | 2017-05-24 16:51:56 | 123 | H | 36.94 |
+----+---------------------+------+-----------+-------+
Temperature and humidity are measured in the same time, so I want this table to be like this:
+---------------------+------+-------+-------+
| meas_time | room | Temp | Humid |
+---------------------+------+-------+-------+
| 2017-05-24 16:51:47 | 123 | 22.61 | 36.93 |
| 2017-05-24 16:51:51 | 123 | 22.61 | 36.94 |
| 2017-05-24 16:51:56 | 123 | 22.61 | 36.94 |
+---------------------+------+-------+-------+
I've tried to make this query, but it gives me an error:
ERROR 1242 (21000): Subquery returns more than 1 row
Please help me to get a correct result.
select
m.meas_time,
m.room,
(select value from meteo m1 where m1.meas_kind='T' and m.meas_time=m1.meas_time) as Temp,
(select value from meteo m2 where meas_kind='H' and m.meas_time=m2.meas_time) as Humid
from meteo m
join meteo m1
on m.meas_time=m1.meas_time
and m.room=m1.room
join meteo m2
on m.meas_time=m2.meas_time
and m.room=m2.room
group by m.room, m.meas_time;

Answer 1

You are overcomplicating things. A simple pivot query can give you the results you want.
SELECT
meas_time,
room,
MAX(CASE WHEN meas_kind = 'T' THEN value END) AS Temp,
MAX(CASE WHEN meas_kind = 'H' THEN value END) AS Humid
FROM meteo
GROUP BY meas_time, room