Appropriate use of a junction table? - mysql

Question

I need to record or match one or more rows in one table to one or more rows in another table. I think this works with a third table (a junction table), but not certain.
Not concerned about speed or anything fancy like that atm, just a reliable table design. The two important reporting elements here are:
being able to generate paycheque hours AND a list of tasks performed on same report
to tell who worked on each task (since the data may come in without individual hours (ie a team spent x number of hours on the task), we won't always be able to narrow down exactly how much each employee on a team spent on one task, we are fine with this limitation).
Here is an example:
"HOURS TABLE" records hours worked.
Fred and Joe each work 8 hours on day 1 - so this is two rows in the db
Frank worked 8 hours on day 2
"HOURS TABLE"
eeid hours junction
1 8 1
2 8 1
3 8 2
Second table records what was worked on (Called units table but actually want to record the hours to a task).
Day 1, Fred and Joe built a bench (12hrs), drove around (3hrs) and cleaned up the shop (1hr) - So this is three rows in the table "TASK TABLE"
Day 2, Marilyn spent 8 hours on the same bench, one row in "TASK TABLE"
"TASK TABLE"
ItemID hours junction
1 12 1
2 3 1
3 1 1
1 8 2
Third table is the "JUNCTION TABLE", serves no other purpose except to tie it all together, this is the junction table
"JUNCTION TABLE"
ID
1
2
Issues :
Fred and joe might be a team of 1 or a team of 10.
Multiple employees may work on the same things (like building a bench), and need to tie each row in the "TASK TABLE" to the row(s) in the "HOURS TABLE"
Not sure the junction table should just be a reference, wikipedia shows an example where it is actually storing data, but i don't think that would be appropriate here
I don't know how I will write the query to do my reports mostly because i have never used a junction table before, can't imagine it is that much harder.....
I suppose I could suggest that we force the employees to give separate time sheets, this would remove all of these challenges, as one record could record the hours per task and those records could be summed by day to get the daily hours. - Don't know how bad a junction table is to know if this should be suggested.

Answer 1

Many-to-many relationships in SQL require a JOIN table. Foreign key constraints can only model 1-to-many relationships, so you need one for each side.
Your requirements are confusing, but here's a simple example where one or more USER can be assigned to one or more UNIT:
create table user (
id int not null auto_increment,
primary key(id)
);
create table unit (
id int not null auto_increment,
primary key(id)
);
create table user_unit (
user_id int,
unit_id int,
primary key(user_id, unit_id),
foreign key user_id references user(id),
foreign key unit_id references unit(id)
);