Sets a cluster key when creating a table.
Cluster key is intended to improve query performance by physically clustering data together. For example, when you set a column as your cluster key for a table, the table data will be physically sorted by the column you set. This will maximize the query performance if your most queries are filtered by the column.
CREATE TABLE <name> ... CLUSTER BY ( <expr1> [ , <expr2> ... ] )
This command creates a table clustered by columns:
CREATE TABLE t1(a int, b int) CLUSTER BY(b,a);