UUID datatype for IBMi

A UUID is a Universally Unique Identifier, meaning that these identifiers are unique over your whole DB; even better unique" across space and time". UUID's are stored in 128bit format and follow a standarized format (rfc4122) This makes the type a great alternative to the ID as identity column, I would dare say a superior alternative.

Advantages

• Easy replications

  • Move data from one system to another

    • Possible because the UUID contains the mac-address of the system. This mac-address should be unique for every system.

    • This makes data-integration between 2 systems effortless

  • Move data from one lib to another

    • The libs are DB2 specific

    • A system where imports between libs are also that easy would be nice. With only UUID's it is still a tedious task. (Similar to the problems we have with ID's now)

• Generated randomly, impossible to guess the previous/next value

  • Very important in the context of API's since most API protocols expose their unqiue keys in the url.

    • REST

    • OpenAPI

  • Developers don't have to worry about encrypting/hashing their keys. (Imagine click & print coupons where you could guess the next value...)

• Supported by almost every respected ORM (sometimes even the default over ID)

• Add the advantages of regular ID's to this list...

What would the UUID implementation look like? (Pseudocode)

Solution similar to the id:

CREATE OR REPLACE TABLE USERS  (

    uuid uuid not null generated always as identity,

    firstname varchar(50) not null,

    lastname varchar(50) not null



   primary key (uuid)

);

An alternative would be to combine GENERATED ALWAYS with DEFAULT GENERATE_UUID(): 

CREATE OR REPLACE TABLE USERS  (

    uuid varchar(50) generated always default GENERATE_UUID(),

    firstname varchar(50) not null,

    lastname varchar(50) not null



   primary key (uuid)

);

My least favorite alternative is provide a default so applications don't have to pass the value every time. But it allows invalid userinput: 

CREATE OR REPLACE TABLE USERS  (

    uuid varchar(50) not null default GENERATE_UUID(),

    firstname varchar(50) not null,

    lastname varchar(50) not null



   primary key (uuid)

);

Note: It seems like we can't use scalar functions like GENERATE_UNIQUE() as default value today. Is this material for a separate ticket?

Workarounds/Alternatives (See attached SQL files to play with it yourself)

Rowid

GUID/UUID identity support

Support for UUID columns

CREATE OR REPLACE TABLE USERS  (

    rid rowid generated always,

    firstname varchar(50) not null,

    lastname varchar(50) not null

);



insert into users (firstname, lastname)

values ('Mario', 'Aquino'), ('Dimi', 'VLH');



-- Does NOT work => only one rowid/table allowed

CREATE OR REPLACE TABLE ADDRESSES (

    rid rowid generated always,

    street varchar(50),

    city varchar(50),

    user_id rowid,

    

    foreign key (user_id) REFERENCES users(rid)

);



-- Does not work because the types are not compatible?

CREATE OR REPLACE TABLE ADDRESSES (

    rid rowid generated always,

    street varchar(50),

    city varchar(50),

    user_id varchar(26),

    

    foreign key (user_id) REFERENCES users(id)

);

• No primary-/foreign-key constraints possible

• Does not work (maybe with some complex casting?)

Triggers

CREATE OR REPLACE TABLE USERS  (

    uuid varchar(13) not null,

    firstname varchar(50) not null,

    lastname varchar(50) not null,



   primary key (uuid)

);



CREATE OR REPLACE TRIGGER generate_uuid AFTER INSERT ON USERS FOR EACH ROW MODE DB2SQL UPDATE USERS SET UUID = GENERATE_UNIQUE();



insert into users (uuid, firstname, lastname)

values ('tempstring', 'Mario', 'Aquino'), ('tempstring2', 'Dimi', 'VLH');



select *

from users;

• SQL adapters in Open Source Languages will have to check if the trigger exists before every insert operation.

• On insert we have to send dummydata in the table as a placeholder before the trigger is executed. For an identity column it becomas a daunting task to provide unique dummydata.

Alternative with SQL Sequence Object

CREATE OR REPLACE TABLE USERS  (

    uuid integer not null,

    firstname varchar(50) not null,

    lastname varchar(50) not null,

    

    primary key (uuid)

);



CREATE OR REPLACE SEQUENCE unique_identifiers AS INTEGER

  START WITH 1

  INCREMENT BY 1

  NO MAXVALUE

  NO CYCLE

  CACHE 20;



-- Does not work, because the uuid is not generated  

insert into users (firstname, lastname)

values ('Mario', 'Aquino'), ('Dimi', 'VLH');



insert into users (uuid, firstname, lastname)

values (next value for unique_identifiers, 'Mario', 'Aquino'), (next value for unique_identifiers,'Dimi', 'VLH');



select *

from users;

• External users can guess the next key (still just incrementing numbers)

• SQL adapters in Open Source languages will have to check if this sequence exists before every insert.

What about other databases?

Postgresql has great support for this column type.

MySQL and SQLite stumble behind, but their connector-packages provide support from within the OpenSource languages. I'm not a fan of this approach since you have to translate the logic to every language...

Recap

I know there have been tickets opened about this before. But today we still don't have proper working workarounds, are they are too much work to implement and maintain.

UUID's appear more and more into modern implementations because it guaranties easier integration in future systems because you can use the existing identifiers. No need to create mapping between identifiers from system A to system B!