Unique ID Examples

⸺ by Charles Iliya Krempeaux

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Let's look at some examples of unique IDs to try to make some of this clearer.

School ID

In some parts of the world, when you attend a school as a student, you are assigned a special number that is often called something like your student ID.

Each new student that attends the school is given their own student ID. And once a student is assigned a particular student ID, no other student will ever be given that student ID.

This student ID is a unique ID.

Let's look at an example school, to see what I mean. Let's make up a school, for the sake of this example: 

	Fanstasy College

At Fantasy College, the staff at the school will assign to each new student a student ID made up of the following 4 pieces of information: 

	[YEAR] [MONTH] [CAMPUS] [SEQUENCE-NUMBER]

So, for example, if when the new student joined Fantasy College, we had:

I.e., this new student is the 8750th student to join the school in September 1995 at campus 0000.

Or in other words: 

	[YEAR] [MONTH] [CAMPUS] [SEQUENCE-NUMBER]
	 1995    09      000        08750

They could write the Fantasy College student ID for this new student as: 

	1995-09-000-08750

Or maybe, alternatively, could more compactly write it as (if each part was always the same number of characters): 

	19950900008750

What about the next new student to join Fantasy College at campus `000` in September 1995? Well, that new student would be the 8751st student, and would be assigned the student ID: 

	19950900008751

Etc.

Here are some more example student IDs: 

	| Student ID     | Year | Month | Campus | Sequence Number |
	|----------------|------|-------|--------|-----------------|
	| 19950900008750 | 1995 | 09    | 000    | 08750           |
	| 19950900008751 | 1995 | 09    | 000    | 08751           |
	| 19950900005005 | 1995 | 09    | 000    | 05005           |
	| 19960500012269 | 1996 | 05    | 000    | 12269           |
	| 20000900118727 | 2000 | 09    | 001    | 18727           |
	| 20220100421008 | 2022 | 01    | 004    | 21008           |

So, in the domain of Fantasy College, the student ID is a unique ID.

Database Primary-Key

Another example of a locally unique identifier (unique ID) is a primary-key in a database table.

For example with the Postgres database, primary-keys often have positive integer values such as — 1, 2, 3, 4, 5, etc. Within a single table these primary-key values are unique. But other tables might also use those exact same values for its own primary-keys.

For example, imagine you have a users table that uses positive integer unique IDs like so: 

	| ID | username     |
	|----|--------------|
	|  1 | joeblow      |
	|  2 | janedoe      |
	|  3 | johndoe      |
	|  4 | hjsimpson    |
	|  5 | brucebanner  |

And also, for example, imagine you have a products table that uses positive integer unique IDs like so: 

	| ID  | name     | price |
	|-----|----------|-------|
	|  1  | Skeletor | $14   |
	|  2  | Panthor  | $19   |
	|  3  | Moss-Man | $14   |
	|  4  | Webstor  | $14   |
	|  5  | Spikes   | $14   |

ID 1 is a nickname for joeblow in the users table, but ID 1 is also a nickname for Skeletor in the products table.

The same IDs are used in both tables, but have different meanings in each table.

If I just told you the ID is 5, you wouldn't know if I'm referring to brucebanner (in the users table) or Spikes (in the products table), unless I also told you which table I was referring to.

So, in the domain of this particular products table, the ID primary-key is a unique ID.

UUID

The intent of UUIDs is that they are more broadly unique.

Let's look at what would happen if we instead used UUIDs for the primary-keys.

So, for example, imagine you have a users table that uses UUID as unique IDs like so: 

	| ID                                   | username     |
	|--------------------------------------|--------------|
	| 37bd2273-f442-4520-b2f7-7402eaab36c2 | joeblow      |
	| 0b2bb6fb-27d4-49c6-8aad-304c015e1df5 | janedoe      |
	| a1192fd5-1fef-4054-8c44-5cf71e217283 | johndoe      |
	| 84e60040-0f74-4a2a-9451-d068aa260c9d | hjsimpson    |
	| 8cff54ab-d888-4613-8363-dc264ff2937f | brucebanner  |

And also, for example, imagine you have a products table that uses UUID as unique IDs like so: 

	| ID                                     | name     | price |
	|----------------------------------------|----------|-------|
	| `39bf9f7d-00ce-41e2-8645-75ffd4f65458` | Skeletor | $14   |
	| `496bb0fe-2957-4d52-b48c-56e7fcb0c9e9` | Panthor  | $19   |
	| `5b3a831c-9d64-42ad-82e4-fb734599bbda` | Moss-Man | $14   |
	| `25197b99-655e-430c-9446-e991a874870f` | Webstor  | $14   |
	| `dd001ac2-0c65-4b06-8a8a-8b98097b634f` | Spikes   | $14   |

If I just told you the ID is dd001ac2-0c65-4b06-8a8a-8b98097b634f, you wouldn't need me to tell you which table I was referring to, since it is unique across all tables.

You would know, just with that UUID, that I was referring to the products table, and in particular, I was referring to Spikes.