JOINing databases with SQLite - r

Question

I have 4 databases relating to the America's Cup.
SELECT * FROM teams
>
Code | Country | TeamName
ITA |Italy | Luna Rossa Prada Pirelli Team
NZ |New Zealand | Emirates Team New Zealand
UK |United Kingdom | INEOS Team UK
USA |United States of America | NYYC American Magic
4 rows
SELECT * FROM races
>
Race Tournament Date Racedate
RR1R1 RR 15-Jan 18642
RR1R2 RR 15-Jan 18642
RR1R3 RR 16-Jan 18643
RR2R1 RR 16-Jan 18643
RR2R2 RR 17-Jan 18644
RR2R3 RR 17-Jan 18644
RR3R1 RR 23-Jan 18650
RR3R2 RR 23-Jan 18650
RR3R3 RR 23-Jan 18650
SFR1 SF 29-Jan 18656
1-10 of 31 rows
SELECT * FROM tournaments
>
Tournament Event TournamentName
RR Prada Cup Round Robin
SF Prada Cup Semi-Final
F Prada Cup Final
AC America's Cup Americas Cup
4 rows
SELECT *
FROM results
>
Race Code Result
FR1 ITA Win
FR1 UK Loss
FR2 UK Loss
FR2 ITA Win
FR3 UK Loss
FR3 ITA Win
FR4 ITA Win
FR4 UK Loss
FR5 ITA Win
FR5 UK Loss
1-10 of 62 rows
and I'm trying to write an SQL query that will output the number of races each team won by tournament, and show the output. The output table should include the full name of the Event, the Tournament and the full name of each team. My query at the moment looks like this:
SELECT TeamName, Result, Event, tournaments.Tournament
FROM teams LEFT JOIN results
ON teams.Code = results.Code
LEFT JOIN races
ON results.Race = races.Race
LEFT JOIN tournaments
ON races.Tournament = tournaments.Tournament
WHERE Result = 'Win'
ORDER BY tournaments.Tournament
which outputs:
TeamName Result Event Tournament
Emirates Team New Zealand Win America's Cup AC
Emirates Team New Zealand Win America's Cup AC
Luna Rossa Prada Pirelli Team Win America's Cup AC
Luna Rossa Prada Pirelli Team Win America's Cup AC
Emirates Team New Zealand Win America's Cup AC
Luna Rossa Prada Pirelli Team Win America's Cup AC
Emirates Team New Zealand Win America's Cup AC
Emirates Team New Zealand Win America's Cup AC
Emirates Team New Zealand Win America's Cup AC
Emirates Team New Zealand Win America's Cup AC
When I try to COUNT(Result) AS NumberOfWins, I get:
TeamName Result NumberOfWins Event Tournament
Luna Rossa Prada Pirelli Team Win 31 Prada Cup F
1 row
Why does adding the count count only Luna Rossa's wins? How can I change the query to fix it?

Answer 1

Why does adding the count count only Luna Rossa's wins?
Count() is an aggregate function and produces one result per GROUP.
As you have no GROUP BY clause the entire result set is a single group and hence the single result.
The reason why you got Tournament F is due to
If the SELECT statement is an aggregate query without a GROUP BY clause, then each aggregate expression in the result-set is evaluated once across the entire dataset. Each non-aggregate expression in the result-set is evaluated once for an arbitrarily selected row of the dataset. The same arbitrarily selected row is used for each non-aggregate expression. Or, if the dataset contains zero rows, then each non-aggregate expression is evaluated against a row consisting entirely of NULL values. As per SQLite SELECT -
How can I change the query to fix it?
So you need a GROUP BY clause. To create groups upon which the count() function will work on.
You probably want GROUP BY Tournament,TeamName
e.g.
SELECT TeamName, Result, Event, tournaments.Tournament, count(*)
FROM teams LEFT JOIN results
ON teams.Code = results.Code
LEFT JOIN races
ON results.Race = races.Race
LEFT JOIN tournaments
ON races.Tournament = tournaments.Tournament
WHERE Result = 'Win'
GROUP BY Tournament,Teamname
ORDER BY tournaments.Tournament