Having difficulty in constructing SQL query for events - mysql

Question

I have a problem where I'm trying to get counts of data associated with multiple events occurring on separate days.
Let's say I'm following a group of plane-spotters, each of whom may spot many planes from around the world on any one day, while based at some particular airport. I'd like to produce a list consisting of one row per spotter per day, with columns for the spotter's ID, the date, how many planes he (it's always "he", right?) spotted on that day, how many individual airlines the planes belonged to, and how many countries the airlines belonged to. So, I'd like to have results like this:
+-----------+------------+---------+----------+-----------+
| | | Planes | | Airline |
| SpotterID | Date | spotted | Airlines | Countries |
+-----------+------------+---------+----------+-----------+
| 1234 | 2017-04-15 | 28 | 11 | 4 |
+-----------+------------+---------+----------+-----------+
| 1234 | 2017-04-16 | 65 | 19 | 7 |
+-----------+------------+---------+----------+-----------+
| 5678 | 2017-04-22 | 39 | 14 | 6 |
+-----------+------------+---------+----------+-----------+
| 6677 | 2017-04-28 | 74 | 29 | 9 |
+-----------+------------+---------+----------+-----------+
So, (MySQL 5.7.17) my test tables are as sketched out below (I may have forgotten a couple of indexes).
The plane-spotting events table is defined as:
CREATE TABLE `SpottingEvents` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`SpotterID` int(11) NOT NULL,
`SpotDateTime` datetime NOT NULL,
`PlaneID` int(11) NOT NULL,
`Notes` varchar(100) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `indx_SpotterID_PlaneID_DateTime` (`SpotterID`,`PlaneID`,`SpotDateTime`),
KEY `indx_SpotterID_DateTime` (`SpotterID`,`SpotDateTime`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8
the planes table is defined as:
CREATE TABLE `Planes` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`PlaneID` int(11) NOT NULL,
`PlaneTypeID` int(11) NOT NULL,
`AirlineID` int(11) NOT NULL,
`Notes` varchar(100) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `indx_PlaneID_AirlineID` (`PlaneID`,`AirlineID`),
) ENGINE=InnoDB DEFAULT CHARSET=utf8
the airlines table is defined as:
CREATE TABLE `Airlines` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`AirlineID` int(11) NOT NULL,
`AirlineName` varchar(100) NOT NULL,
`CountryID` int(11) NOT NULL,
`Notes` varchar(100) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `indx_AirlineID` (`AirlineID`),
) ENGINE=InnoDB DEFAULT CHARSET=utf8
and the countries table is defined as:
CREATE TABLE `Countries` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`CountryID` int(11) NOT NULL,
`CountryName` varchar(100) NOT NULL,
`Notes` varchar(100) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `indx_CountryID` (`CountryID`),
) ENGINE=InnoDB DEFAULT CHARSET=utf8
My problem is with the last two columns, the Airlines and Countries counts. I've tried several ways to do this, including the following:
select distinct sev.SpotDateTime, sev.SpotterID, count(*) as planes_count,
(select count(*) from ( select distinct cnt.CountryID
from Countries as cnt
inner join Airlines as aln on al.CountryID = cnt.CountryID
inner join Planes as pl on pl.AirlineID = aln.AirlineID
where pl.PlaneID = sev.PlaneID ) as t1) as countries_count
from SpottingEvents as sev
# where sev.UserID = 1234
group by SpotDateTime
order by SpotDateTime
which leads to an error Unknown column 'sev.planeID' in 'where clause'
but since I'm no expert, I'm just not getting the intended results. So, how do I achieve the desired results?

Answer 1

You are looking for COUNT(DISTINCT). Join the tables needed, then count.
select
se.spotterid,
date(se.spotdatetime) as spot_date,
count(*) as planes,
count(distinct p.airlineid) as airlines,
count(distinct a.countryid) as countries
from spottingevents se
join planes p on p.planeid = se.planeid
join airlines a on a.airlineid = p.airlineid
group by se.spotterid, date(se.spotdatetime)
order by date(se.spotdatetime), se.spotterid;