Composite primary key or not?

Question

Here\'s what\'s confusing me. I often have composite primary keys in database tables. The bad side of that approach is that I have pretty extra work when I delete or edit en

Answer 1

I personally prefer your 2nd approach (and would use it almost 100% of the time) - introduce a surrogate ID field.

Why?

• makes life a lot easier for any tables referencing your table - the JOIN conditions are much simpler with just a single ID column (rather than 2, 3, or even more columns that you need to join on, all the time)

• makes life a lot easier since any table referencing your table only needs to carry a single ID as foreign key field - not several columns from your compound key

• makes life a lot easier since the database can handle the creation of unique ID column (using INT IDENTITY)

However, I do not know how they preserve uniqueness of data entries.

Very simple: put a UNIQUE INDEX on the compound columns that you would otherwise use as your primary key!

CREATE UNIQUE INDEX UIX_WhateverNameYouWant 
   ON dbo.ProxUsingDept(fkProx, fkDept)

Now, your table guarantees there will never be a duplicate pair of (fkProx, fkDept) in your table - problem solved!