簇是用来存储表的方法,这些表互相联系密切,通常相连在磁盘的相同区域上 ,簇共享同一列的一组表，用于检索时提高效率 -Cluster method is used to store tables, these tables are closely interrelated, often linked in the same area on the disk, the cluster out of a group sharing the same table for retrieval efficiency