Question

我遇到了一个sql代码，我需要按照以下方式获取数据（我希望我能解释得足够好）：我的数据库中有三个表：

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)

我需要计算下雨的事故数量。表格的关键是：

From 1 to 2: VKL_NUMBER(accident number)
From 2 to 3: STN_NUMBER (weather station number)

我怎样才能获得当时最接近事故的风雨类型喜欢：

Count accidents where it rains at the closest weatherstation.

了解更多信息：

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

我假设你想要在事故发生之前的车站时间。打破关系是一个重大的复杂因素，我们需要更多关于您所需的匹配逻辑的信息。

SQL从表1中获取计数复杂

1 个答案: