Question

I have a one-to-many relationship between two classes for this situation. I have a swimming competition and that competition can have x swimmers.

How can I create an SQL table for this, I know I will have to use the Primary Key of Swimmers as a foreign key in the Swimming competition but I have no idea how to represent the correct number of attributes since it’s unknown.

Answer 1

This is called a m:n relationship and usually solved with a mapping table.

Something like this:

create table swimmer 
(
   id         integer not null primary key,
   lastname   varchar(100) not null,
   firstname  varchar(100)
)

create table competition 
(
   id        integer not null primary key,
   name      varchar(50) not null,
   comp_date date not null
)

create table participant
( 
   swimmer_id           integer not null, 
   competition_id       integer not null, 
   rank_in_competetion  integer,  
   primary key (swimmer_id, competition_id), 
   constraint fk_participant_swimmer (swimmer_id) references swimmer(id),
   constraint fk_participant_competition (competition_id) references competition(id)
)