SQL - Teams and Their Player Count - sql

Question

I'd need some help here. Im stuck on this SQL Query.
I have 2 Tables team and function. Team contains ID,Teamname. Function contains ID,Role
role decides whether a person is a player or a coach (0 for player, 1 for coach).
I am supposed to list all teams that exists, but they should only count players and even teams with no players should be listed to. There's teams that only have coaches for example.
i can't find any way to count everyone within a team.
This is the closest I've come:
select teamname,
count(*)
from function left outer join team on team.id = function.id
WHERE role=0
group by teamname;

Answer 1

Here's one way to get the result:
SELECT t.teamname
, COUNT(1) AS player_count
FROM team t
LEFT
JOIN function f
ON f.id = t.id
AND f.role = 0
GROUP BY t.teamname;
-- or --
SELECT t.teamname
, IFNULL(SUM(f.role=0),0) AS player_count
FROM team t
LEFT
JOIN function f
ON f.id = t.id
GROUP BY t.teamname;
These queries use the team table as the driver, so we get rows from team even when there isn't a matching row in function. In the first query, we include the role=0 condition as a join predicate, but it's an outer join. In the second query, it's still an outer join, but we only "count" rows that have role=0.
NOTE It looks as if something is missing from your model; the id=id join predicate looks odd; it's odd that we'd have a column named id in the function table which is a foreign key referencing team.id.
Normally, id is the surrogate primary key in a table, and it's unique in that table. If it were unique in the function table, then that implies a one-to-one relationship between team and function, and the query will never return a count greater than 1.
Again, I strongly suspect that the "member" entity is missing from the model.
What we'd expect is something like this::
team
id PK
teamname
member
id PK
team_id FK references team.id
role 0=player, 1=coach
such that the query would look something like this:
SELECT t.teamname
, IFNULL(SUM(m.role=0),0) AS player_count
, IFNULL(SUM(m.role=1),0) AS coach_count
FROM team t
LEFT
JOIN member m
ON m.team_id = t.id

Answer 2

You can't select a single column when an aggregate function exists in the SELECT clause.
To get a count of all rows in the table and get the name of the team, you must use only aggregated columns or functions in the SELECT clause. For example:
SELECT COUNT(*), team.teamname
FROM function LEFT OUTER JOIN team ON team.id = function.id
WHERE function.role = 0
GROUP BY team.teamname
Gives you a total of all rows where role is equal to 0 plus the name of the team.

Answer 3

Use the following instead:
SELECT teamname,SUM(IF(role=0,1,0)) players
FROM function
LEFT JOIN team USING (id)
GROUP BY teamname;
This counts only those entries from 'function' that have player role (0).