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

You ask the following questions:

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

Uniqueness can be preserved by declaring a separate composite UNIQUE index on columns that would otherwise form the natural primary key.

Which way is better?

Different people have different opinions, sometimes strongly held. I think you will find that more people use surrogate integer keys (not that that makes it the "right" solution).

What are the bad sides of using the 2nd approach?

Here are some of the disadvantages to using a surrogate key:

1. You require an additional index to maintain the unique-ness of the natural primary key.

2. You sometimes require additional JOINs to when selecting data to get the results you want (this happens when you could satisfy the requirements of the query using only the columns in the composite natural key; in this case you can use the foreign key columns rather than JOINing back to the original table).