Based on the definition, a Junction Table (bridge table/link table) can be used for a lot of-to-many associations, when used such as this:
CREATE TABLE Users ( UserLogin varchar(50) PRIMARY KEY, UserPassword varchar(50) NOT NULL, UserName varchar(50) NOT NULL ) CREATE TABLE Permissions ( PermissionKey varchar(50) PRIMARY KEY, PermissionDescription varchar(500) NOT NULL ) --This is the junction table. CREATE TABLE UserPermissions ( UserLogin varchar(50) REFERENCES Users (UserLogin), PermissionKey varchar(50) REFERENCES Permissions (PermissionKey), PRIMARY KEY (UserLogin, PermissionKey) )
But could not it also be employed just like easily for any one-to-many associations, as with this situation by which one user is connected with lots of orders:
(I do not understand databases well so please correct me basically have misinterpreted something.)
CREATE TABLE Users ( UserLogin varchar(50) PRIMARY KEY, UserPassword varchar(50) NOT NULL, UserName varchar(50) NOT NULL ) CREATE TABLE Orders ( OrderKey varchar(50) PRIMARY KEY, OrderDescription varchar(500) NOT NULL ) --This is the junction table. CREATE TABLE UserOrders ( UserLogin varchar(50) REFERENCES Users (UserLogin), OrderKey varchar(50) REFERENCES Orders (OrderKey), PRIMARY KEY (UserLogin, OrderKey) )
There's no reason a junction table could not be utilized for any one-to-many relationship. Now you ask , usually among performance. Why result in the database join one more table when it's unnecessary?
Yes, however you depart the make sure that it isn't many to a lot of towards the application, rather than enforcing it within the database.
Once you have built a table, it truly does not have a kind of "Junction" table, "associative" table, "join" table -- it is simply a table.
We begin using these terms to explain a particular reason an entity (and resulting table) was produced. Associative organizations are produced, initially, to solve a many-to-many situation. However these tables quite frequently have characteristics that belongs to them (like the duration of the association, grounds for that association, etc.). So SQL Server, Oracle or perhaps your code doesn't have reason to understand why a table was produced...just it's a table.
From the technical perspective, there really is not any distinction between an associative table and then any other table.
So these tables can fill any role that every other table can fulfill. You will find no rules around how other tables may also be associated with them.