1. A method for clustering a target table in a relational database management system, the method comprising: receiving a statement to define the target table; wherein the statement specifies clustering criteria; wherein the clustering criteria specifies one or more columns by which data rows of the target table are to be ordered within contiguous disk blocks; wherein at least one of the one or more columns by which data rows of the target table are to be ordered within contiguous disk blocks is a column of a table other than the target table; wherein the clustering criteria specifies join criteria, the join criteria comprising a foreign key column of the target table and a unique key column of the other table; in response to receiving a command to load particular data rows into the target table, ordering the particular data rows within contiguous disk blocks based on values in the one or more columns and according to the clustering criteria; wherein the ordering the particular data rows within contiguous disk blocks based on values in the one or more columns and according to the clustering criteria comprises joining the particular data rows with rows of the other table according to the join criteria; and wherein the method is performed by one or more computing devices.