Database Reference
In-Depth Information
Table and column options
The table creation statement given in the previous section is very simple: little more than a
list of column names and their respective types. In contrast, an SQL
CREATE TABLE
statement will often look quite complex, with multiple options set on each column, such as
defaults, constraints, and nullability flags. What sorts of bells and whistles can we add to a
CQL table?
At the table level, Cassandra does have quite a few configuration options, known as
table
properties
. These properties allow you to tune a wide range of under-the-hood aspects of
the table, such as caching, compression, garbage collection, and read repair. Table proper-
ties do not, however, bear on the table's behavior from the application's standpoint. For this
reason, we won't go into detail about them in this topic.
Columns, on the other hand, have very few knobs to turn. In fact, outside of the type, each
column is pretty much the same. There are several column options you may be accustomed
to from SQL databases that don't carry over to Cassandra, such as the following:
• Cassandra doesn't have a concept of
NULL
values; columns either have data, or
they don't. Primary key columns are always required to have a value; non-key
columns are always optional. You will see the word
null
appear in the cqlsh out-
put, but that simply means there is no data in this column, and should not be con-
fused with the concept of
NULL
in a relational database.
• Cassandra doesn't support default values for columns. If a row is inserted without a
value for a certain column, that column just doesn't have a value.
• Cassandra doesn't provide data validations like length limits or other more com-
plex column constraints. As long as a value is of the right type for the column
you're putting it in, it's valid.
Happily, most modern applications do not need to rely on the sorts of constraints listed
above; domain modeling libraries and object mappers typically allow you to easily apply
these constraints at the application level.
