Oracle:

CREATE CLUSTER

CREATE CLUSTER [ schema. ] cluster
(column datatype [ SORT ]
[, column datatype [ SORT ] ]...
)
[ { physical_attributes_clause
| SIZE size_clause
| TABLESPACE tablespace
| { INDEX
| [ SINGLE TABLE ]
HASHKEYS integer [ HASH IS expr ]
}
}...
]
[ parallel_clause ]
[ NOROWDEPENDENCIES | ROWDEPENDENCIES ]
[ CACHE | NOCACHE ] ;

physical_attributes_clause::=
[ { PCTFREE integer
| PCTUSED integer
| INITRANS integer
| storage_clause
}...
]
parallel_clause ::=
{ NOPARALLEL | PARALLEL [ integer ] }

example

CREATE CLUSTER personnel
(department NUMBER(4))
SIZE 512
STORAGE (initial 100K next 50K);

CREATE INDEX idx_personnel ON CLUSTER personnel;

CREATE TABLE dept_10
CLUSTER personnel (department_id)
AS SELECT * FROM employees WHERE department_id = 10;

CREATE TABLE dept_20
CLUSTER personnel (department_id)
AS SELECT * FROM employees WHERE department_id = 20;

CREATE CLUSTER language (cust_language VARCHAR2(3))
SIZE 512 HASHKEYS 10
STORAGE (INITIAL 100k next 50k);

CREATE CLUSTER address
(postal_code NUMBER, country_id CHAR(2))
HASHKEYS 20
HASH IS MOD(postal_code + country_id, 101);

CREATE CLUSTER cust_orders (customer_id NUMBER(6))
SIZE 512 SINGLE TABLE HASHKEYS 100;