How to auto generate uuid in cassandra CQL 3 command line

问题

Just learning cassandra, is there a way to insert a UUID using CQL, ie

create table stuff (uid uuid primary key, name varchar);
insert into stuff (name) values('my name'); // fails
insert into stuff (uid, name) values(1, 'my name'); // fails

Can you do something like

insert into stuff (uid, name) values(nextuid(), 'my name');

回答1:

You can with time uuids (type 1 UUID) using the now() function e.g.

insert into stuff (uid, name) values(now(), 'my name');

Works with uid or timeuuid. It generates a "guaranteed unique" UID value, which also contains the timestamp so is sortable by time.

There isn't such a function for type 4 UUIDs though.

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UPDATE: This note pertains to older versions of Cassandra. For newer versions, see below.

回答2:

As of Cassandra 2.0.7 you can just use uuid(), which generates a random type 4 UUID:

INSERT INTO users(uid, name) VALUES(uuid(), 'my name');

回答3:

Actually there is a way to do that using the blob conversion functions - blobAsType() and typeAsBlob(). In your case this should be:

insert into stuff (uid, name) values(blobAsUuid(timeuuidAsBlob(now())), 'my name');

This converts timeuuid to blob and from the blob converts it to uuid.

回答4:

A UUID is a Universally Unique ID used to avoid collisions.

Cassandra 2.0.7 and later versions include the uuid() function that takes no parameters and generates a Type 4 UUID for use in INSERT or SET statements.

You can also use a timeuuid type with a function like now(). They generate a Type 1 UUID.

The difference between Type 1 and Type 4 UUIDs is that a Type 1 UUID is generated using a timestamp and a Type 4 is generated using random numbers.

If you want to use a timeuuid as a uuid use something like blobAsUuid(timeuuidAsBlob(now())), since the value returned by now() is guaranteed to be unique.

References:

http://docs.datastax.com/en/cql/3.3/cql/cql_reference/uuid_type_r.html

http://docs.datastax.com/en/cql/3.3/cql/cql_reference/timeuuid_functions_r.html

http://docs.datastax.com/en/cql/3.3/cql/cql_reference/blob_r.html

来源：https://stackoverflow.com/questions/17945341/how-to-auto-generate-uuid-in-cassandra-cql-3-command-line