Use a common table with many to many relationship

Question

Hello,
I have two SQL tables: Job and Employee. I need to compare Job Languages Proficiencies and Employee Languages Proficiencies. A Language Proficiency is composed by a Language and a Language Level.
create table dbo.EmployeeLanguageProficiency (
EmployeeId int not null,
LanguageProficiencyId int not null,
constraint PK_ELP primary key clustered (EmployeeId, LanguageProficiencyId)
create table dbo.JobLanguageProficiency (
JobId int not null,
LanguageProficiencyId int not null,
constraint PK_JLP primary key clustered (JobId, LanguageProficiencyId)
create table dbo.LanguageProficiency (
Id int identity not null
constraint PK_LanguageProficiency_Id primary key clustered (Id),
LanguageCode nvarchar (4) not null,
LanguageLevelId int not null,
constraint UQ_LP unique (LanguageCode, LanguageLevelId)
create table dbo.LanguageLevel (
Id int identity not null
constraint PK_LanguageLevel_Id primary key clustered (Id),
Name nvarchar (80) not null
constraint UQ_LanguageLevel_Name unique (Name)
create table dbo.[Language]
Code nvarchar (4) not null
constraint PK_Language_Code primary key clustered (Code),
Name nvarchar (80) not null
My question is about LanguageProficiency table. I added an Id has PK but I am not sure this is the best option.
What do you think about this scheme?
Thank You,
Miguel

Answer 1

That should be find as you alread have unique  non clustered index on the other two columns. you can also define this way 
create table dbo.LanguageProficiency (
Id int identity not null,
LanguageCode nvarchar (4) not null,
LanguageLevelId int not null,
constraint PK_LanguageProficiency_Id primary key Nonclustered(LanguageCode, LanguageLevelId)
Create CLUSTERED index CL_ID on dbo.LanguageProficiency(ID)
What you is need is -- FOreign key constraints between these tables. I see that you are columns but are not enforcing Foreign key constraints.. you need those..
Also you have composite primary keys, unless you guarantee that they will ever increasing numbers, it is not useful to define a composite PK.. it leads to page spilts...
Hope it Helps!!