Is ID column required in SQL?

Question

Traditionally I have always used an ID column in SQL (mostly mysql and postgresql).

However I am wondering if it is really necessary if the rest of the columns in ea

Answer 1

Don't confuse the logical model with the implementation.

The logical model shows a candidate key (all columns) which could makes your primary key.

Great. However...

In practice, having a multi column primary key has downsides: it's wide, not good when clustered etc. There is plenty of information out there and in the "related" questions list on the right

So, you'd typically

• add a surrogate key (ID column)
• add a unique constraint to keep the other columns unique
• the ID column will be the clustered key (can be only one per table)
• You can make either key the primary key now

The main exception is link or many-to-many tables that link 2 ID columns: a surrogate isn't needed (unless you have a braindead ORM)

Edit, a link: "What should I choose for my primary key?"

Edit2

For many-many tables: SQL: Do you need an auto-incremental primary key for Many-Many tables?