Database Reference
In-Depth Information
Structuring of tables
Cassandra structures tables in rows and columns, just like a relational database. Also like a
relational database, the columns available to a table are defined in advance. New columns
cannot be added on-the-fly when inserting data, although it's possible to update an existing
table's schema.
Every table defines one or more columns to act as the
primary key
; each row is uniquely
identified by the value(s) in its primary key column(s), and those columns cannot be left
blank in any row. Cassandra does not offer auto-incrementing primary keys; each row,
when created, must be explicitly assigned a primary key by the client. One good way to
structure the primary key is to use a
natural key
, which is a value that is fundamentally
unique for each row you want to store. That's what we do in the
users
table by making
username
, a naturally unique identifier, the primary key.
Note
Before we continue, I should emphasize the importance of using the latest version of Cas-
sandra. Cassandra and CQL have changed substantially over the past few years, and the
current CQL version 3.1 is not backward compatible with older versions of the language.
The examples in this topic target the latest Cassandra version (at the time of writing, 2.1.2);
make sure you're running this version or a newer one.
