Materialized views names are defined by:
view_name ::= re('[a-zA-Z_0-9]+')
You can create a materialized view on a table using a
CREATE MATERIALIZED VIEW statement:
create_materialized_view_statement ::= CREATE MATERIALIZED VIEW [ IF NOT EXISTS ]
select_statementPRIMARY KEY '('
CREATE MATERIALIZED VIEW monkeySpecies_by_population AS SELECT * FROM monkeySpecies WHERE population IS NOT NULL AND species IS NOT NULL PRIMARY KEY (population, species) WITH comment='Allow query by population instead of species';
CREATE MATERIALIZED VIEW statement creates a new materialized view. Each such view is a set of rows which
corresponds to rows which are present in the underlying, or base, table specified in the
SELECT statement. A
materialized view cannot be directly updated, but updates to the base table will cause corresponding updates in the
Creating a materialized view has 3 main parts:
Attempting to create an already existing materialized view will return an error unless the
IF NOT EXISTS option is
used. If it is used, the statement will be a no-op if the materialized view already exists.
By default, materialized views are built in a single thread. The initial build can be parallelized by
increasing the number of threads specified by the property
cassandra.yaml. This property can also be manipulated at runtime through both JMX and the
getconcurrentviewbuilders nodetool commands.
The select statement of a materialized view creation defines which of the base table is included in the view. That statement is limited in a number of ways:
SELECT *isn’t allowed if the base table has static columns).
WHEREclause have the following restrictions:
IS NOT NULLrestriction. No other restriction is allowed.
IS NOT NULLrestriction (or any other restriction, but they must have one).
A view must have a primary key and that primary key must conform to the following restrictions:
So for instance, give the following base table definition:
CREATE TABLE t ( k int, c1 int, c2 int, v1 int, v2 int, PRIMARY KEY (k, c1, c2) )
then the following view definitions are allowed:
CREATE MATERIALIZED VIEW mv1 AS SELECT * FROM t WHERE k IS NOT NULL AND c1 IS NOT NULL AND c2 IS NOT NULL PRIMARY KEY (c1, k, c2) CREATE MATERIALIZED VIEW mv1 AS SELECT * FROM t WHERE k IS NOT NULL AND c1 IS NOT NULL AND c2 IS NOT NULL PRIMARY KEY (v1, k, c1, c2)
but the following ones are not allowed:
// Error: cannot include both v1 and v2 in the primary key as both are not in the base table primary key CREATE MATERIALIZED VIEW mv1 AS SELECT * FROM t WHERE k IS NOT NULL AND c1 IS NOT NULL AND c2 IS NOT NULL AND v1 IS NOT NULL PRIMARY KEY (v1, v2, k, c1, c2) // Error: must include k in the primary as it's a base table primary key column CREATE MATERIALIZED VIEW mv1 AS SELECT * FROM t WHERE c1 IS NOT NULL AND c2 IS NOT NULL PRIMARY KEY (c1, c2)
After creation, you can alter the options of a materialized view using the
ALTER MATERIALIZED VIEW statement:
alter_materialized_view_statement ::= ALTER MATERIALIZED VIEW
The options that can be updated are the same than at creation time and thus the same than for tables.
Dropping a materialized view users the
DROP MATERIALIZED VIEW statement:
drop_materialized_view_statement ::= DROP MATERIALIZED VIEW [ IF EXISTS ]
If the materialized view does not exists, the statement will return an error, unless
IF EXISTS is used in which case
the operation is a no-op.
Removal of columns not selected in the Materialized View (via
UPDATE base SET unselected_column = null or
DELETE unselected_column FROM base) may shadow missed updates to other columns received by hints or repair.
For this reason, we advise against doing deletions on base columns not selected in views until this is
fixed on CASSANDRA-13826.