如何根据在另一个表中的日期之后加时间戳的行从一个 mysql 表中选择行

Question

My problem downsized to the core part of it, how to show a merged output based on tables date entry.

It's really something else than temperature (and millions of lines) but I made up some numbers here just to illustrate the issue. I have several sensors, each sensor has an id number, each sensor sends out value information at somewhat random intervals. The sensors can move around so I have a separate table (SensorDescriptions) to keep track of when a sensor is moved. Each line there say when a sensor has moved and up until that point it must be considered to be in it's old location (and first entry in SensorDescriptions must be before first recorded value for that sensor).

The desired output is a list of time, sensor-name and value, I entered it in the DesiredOutput table but that is handcrafted (reservation for typos) - I need the query that produce it, "SELECT ... WHERE sv_date BETWEEN $startDate AND $endDate".

Below is a text version of two sample tables (all hand crafted "random" values) and the output (saved a mysqldump at https://pastebin.com/88G77KiM ).

So, what do I write that makes my mysql/mariadb SQL query merge SensorValues and SensorDescriptions so the output is like DesiredOutput?

SensorValues

+---------------------+-------+----------+
| sv_date             | sv_id | sv_value |
+---------------------+-------+----------+
| 2017-01-01 10:00:00 |     1 |       24 |
| 2017-01-01 10:01:00 |     2 |       13 |
| 2017-01-01 10:05:00 |     1 |     24.1 |
| 2017-01-01 10:05:00 |     2 |     13.1 |
| 2017-01-01 10:10:00 |     1 |     24.2 |
| 2017-01-01 10:11:00 |     2 |     13.2 |
| 2017-01-01 10:12:00 |     2 |     13.3 |
| 2017-01-01 10:15:00 |     1 |     24.3 |
| 2017-01-01 10:17:00 |     2 |     13.4 |
| 2017-01-01 10:20:00 |     1 |     24.4 |
| 2017-01-01 10:23:00 |     2 |       -5 |
| 2017-01-01 10:25:00 |     1 |     24.5 |
| 2017-01-01 10:30:00 |     1 |     24.6 |
| 2017-01-01 10:33:00 |     2 |     -5.1 |
| 2017-01-01 10:35:00 |     1 |     -4.7 |
| 2017-01-01 10:37:00 |     2 |     -5.2 |
| 2017-01-01 10:38:00 |     2 |     -5.2 |
| 2017-01-01 10:40:00 |     1 |     -4.8 |
| 2017-01-01 10:41:07 |     1 |     -3.1 |
| 2017-01-01 10:41:07 |     2 |     15.1 |
| 2017-01-01 10:45:00 |     1 |     -4.9 |
| 2017-01-01 10:50:00 |     1 |       -5 |
| 2017-01-01 10:50:00 |     2 |       20 |
| 2017-01-01 10:51:00 |     2 |     20.1 |
+---------------------+-------+----------+

SensorDescriptions

+-------+---------------------+----------------+
| sv_id | sd_date             | sd_description |
+-------+---------------------+----------------+
|     1 | 2017-01-01 09:00:00 | Kitchen        |
|     1 | 2017-01-01 10:32:00 | Garage         |
|     2 | 2017-01-01 09:00:00 | Garage         |
|     2 | 2017-01-01 10:20:00 | Outside        |
|     2 | 2017-01-01 10:40:00 | Basement       |
+-------+---------------------+----------------+

DesiredOutput

+---------------------+----------+-------+
| sv_date             | Location | Value |
+---------------------+----------+-------+
| 2017-01-01 10:00:00 | Kitchen  |    24 |
| 2017-01-01 10:01:00 | Garage   |    13 |
| 2017-01-01 10:05:00 | Garage   |  13.1 |
| 2017-01-01 10:05:00 | Kitchen  |  24.1 |
| 2017-01-01 10:10:00 | Kitchen  |  24.2 |
| 2017-01-01 10:11:00 | Garage   |  13.2 |
| 2017-01-01 10:12:00 | Garage   |  13.3 |
| 2017-01-01 10:15:00 | Kitchen  |  24.3 |
| 2017-01-01 10:17:00 | Garage   |  13.4 |
| 2017-01-01 10:20:00 | Kitchen  |  24.4 |
| 2017-01-01 10:23:00 | Outside  |    -5 |
| 2017-01-01 10:25:00 | Kitchen  |  24.5 |
| 2017-01-01 10:30:00 | Kitchen  |  24.6 |
| 2017-01-01 10:33:00 | Outside  |  -5.1 |
| 2017-01-01 10:35:00 | Garage   |  -4.7 |
| 2017-01-01 10:37:00 | Outside  |  -5.2 |
| 2017-01-01 10:38:00 | Outside  |  -5.2 |
| 2017-01-01 10:40:00 | Garage   |  -4.8 |
| 2017-01-01 10:41:07 | Basement |  15.1 |
| 2017-01-01 10:41:07 | Garage   |  -3.1 |
| 2017-01-01 10:45:00 | Garage   |  -4.9 |
| 2017-01-01 10:50:00 | Basement |    20 |
| 2017-01-01 10:50:00 | Garage   |    -5 |
| 2017-01-01 10:51:00 | Basement |  20.1 |
+---------------------+----------+-------+

---Edit---

I tried the one answer given but end up with errors but after having phpMyAdmin reformatting it I found the typo and got it to work, thanks.

MariaDB [test]> SELECT
    ->     sv_date,
    ->     sd_description AS location,
    ->     sv_value
    -> FROM
    ->     SensorValues sv
    -> INNER JOIN
    ->     (
    ->     SELECT
    ->         sd1.sv_id,
    ->         sd1.sd_date,
    ->         sd1.sd_description,
    ->         COALESCE(
    ->             MIN(sd2.sd_date),
    ->             '9999-12-31 23:59:59'
    ->         ) AS next_sd_date
    ->     FROM
    ->         SensorDescriptions sd1
    ->     LEFT JOIN
    ->         SensorDescriptions sd2
    ->     ON
    ->         sd1.sv_id = sd2.sv_id AND sd1.sd_date < sd2.sd_date
    ->     GROUP BY
    ->         sd1.sv_id,
    ->         sd1.sd_date,
    ->         sd1.sd_description
    -> ) t
    -> ON
    ->     sv.sv_id = t.sv_id AND sv.sv_date >= t.sd_date AND sv.sv_date < t.next_sd_date;
+---------------------+----------+----------+
| sv_date             | location | sv_value |
+---------------------+----------+----------+
| 2017-01-01 10:00:00 | Kitchen  |       24 |
| 2017-01-01 10:05:00 | Kitchen  |     24.1 |
| 2017-01-01 10:10:00 | Kitchen  |     24.2 |
| 2017-01-01 10:15:00 | Kitchen  |     24.3 |
| 2017-01-01 10:20:00 | Kitchen  |     24.4 |
| 2017-01-01 10:25:00 | Kitchen  |     24.5 |
| 2017-01-01 10:30:00 | Kitchen  |     24.6 |
| 2017-01-01 10:35:00 | Garage   |     -4.7 |
| 2017-01-01 10:40:00 | Garage   |     -4.8 |
| 2017-01-01 10:41:07 | Garage   |     -3.1 |
| 2017-01-01 10:45:00 | Garage   |     -4.9 |
| 2017-01-01 10:50:00 | Garage   |       -5 |
| 2017-01-01 10:01:00 | Garage   |       13 |
| 2017-01-01 10:05:00 | Garage   |     13.1 |
| 2017-01-01 10:11:00 | Garage   |     13.2 |
| 2017-01-01 10:12:00 | Garage   |     13.3 |
| 2017-01-01 10:17:00 | Garage   |     13.4 |
| 2017-01-01 10:23:00 | Outside  |       -5 |
| 2017-01-01 10:33:00 | Outside  |     -5.1 |
| 2017-01-01 10:37:00 | Outside  |     -5.2 |
| 2017-01-01 10:38:00 | Outside  |     -5.2 |
| 2017-01-01 10:41:07 | Basement |     15.1 |
| 2017-01-01 10:50:00 | Basement |       20 |
| 2017-01-01 10:51:00 | Basement |     20.1 |
+---------------------+----------+----------+
24 rows in set (0.00 sec)

MariaDB [test]>

Answer 1

For each record in SensorDescriptions table I would get the timestamp of the next location (id any), which would provide the interval that can be used for joining that table to SensorValues table:

select sv_date, sd_description as location, sv_value
from SensorValues sv
inner join
    (select sd1.sv_id,
           sd1.sd_date,
           sd1.sd_description,
           coalesce(min(sd2.sd_date),'9999-12-31 23:59:59') as next_sd_date
    from SensorDescriptions sd1
    left join SensorDescriptions sd2 on sd1.sv_id=sd2.sv_id and sd1.sd_date<sd2.sd_date
    group by sd1.sv_id, sd1.sd_date, sd1.sd_description) t on sv.sv_id=t.sd_id and sv.sv_date>=t.sd_date and sv.sv_date<t.next_sd_date