constraints.rst

Constraints

Columns can be constrained in three ways:

• Primary key
• Not null
• Check

The values of a constrained column must comply with the constraint.

Primary key

The primary key constraint combines a unique constraint and a not-null constraint. It also defines the default routing value used for sharding.

Example:

cr> create table my_table1 (
...   first_column integer primary key,
...   second_column text
... );
CREATE OK, 1 row affected (... sec)

Currently primary keys cannot be auto generated and have to be specified if data is inserted, otherwise an error is returned.

Defining multiple columns with a primary key constraint is also supported:

cr> create table my_table1pk (
...   first_column integer primary key,
...   second_column text primary key,
...   third_column text
... );
CREATE OK, 1 row affected (... sec)

Or using a alternate syntax:

cr> create table my_table1pk1 (
...   first_column integer,
...   second_column text,
...   third_column text,
...   primary key (first_column, second_column)
... );
CREATE OK, 1 row affected (... sec)

Note

Not all column types can be used as PRIMARY KEY.

For further details see :ref:`primary_key_constraint`.

Not null

The not null constraint can be used on any table column and it prevents null values from being inserted.

Example:

cr> create table my_table2 (
...   first_column integer primary key,
...   second_column text not null
... );
CREATE OK, 1 row affected (... sec)

Note

For further details see :ref:`not_null_constraint`.

Check

A check constraint allows you to specify that the values in a certain column must satisfy a boolean expression. This can be used to ensure data integrity. For example, if you have a table to store metrics from sensors and you want to ensure that negative values are rejected:

cr> create table metrics (
...   id TEXT PRIMARY KEY,
...   weight double CHECK (weight >= 0)
... );
CREATE OK, 1 row affected  (... sec)

Note

For further details see :ref:`check_constraint`.