SQL get count from table 1 where complicated - mysql

Question

I am stuck with a sql code where i need te get data as followed(i hope i can explain it good enough):
There are three tables in my database:
Table 1 is filled with traffic accidents(VKL_NUMBER and TIME)
Table 2 is filled with the locations of the accidents and the closest weather station (VKL_NUMBER, LOCATION and STN_NUMBER )
Table 3 is filled with weather data and the weather station where it came from(STN_NUMBER, TIME, WEATHER_TYPE)
I need to count the amount of accidents where it rains.
The keys to the tables are:
From 1 to 2: VKL_NUMBER(accident number)
From 2 to 3: STN_NUMBER (weather station number)
How can i get the weathertype at the time and closest to the accident in a count
Like :
Count accidents where it rains at the closest weatherstation.
for more info:
The accidents table has VKL_NUMBER(FK to the locations table) TIME(HHMM format) and DATE(YYMMDD format)
The locations table has VKL_NUMBER(FK to accidents), LOCATION(not important for this question) and STN_NUMBER(FK to the weather table)
The weather table had STN_NUMBER(FK to locations table), WEATHERTYPE("rain","snow","hail" ), TIME(HHMM format) and DATE(YYMMDD format)

Answer 1

/* apparently you'll need to combine and cast the <date + time> values */
select count(case when weather.weathertype = 'rain' then 1 end)
from
(
select
accidents.vkl_number,
min(<accidents.date + accidents.time>) as time_of_accident,
min(weather.stn_number) as stn_number,
max(timestampdiff(minute,
<weather.date + weather.time>,
<accidents.date + accidents.time>
)) as differential
from
t1 accidents inner join t2 accident_locations
on accident_locations.vkl_number = accidents.vkl_number
inner join t3 weather
on weather.stn_number = accident_locations.stn_number
and weather.time <= accidents.time
group by accidents.vkl_number
) closest
inner join t3 weather
on weather.stn_number = closest.stn_number
and date_add(
<weather.date + weather.time>,
interval differential second
) = closest.time_of_accident
I'm assuming you want the station time just prior to the accident. Breaking ties is a significant complication and we need more info about your desired matching logic.