SAP数据字典中透明表、池表和簇表的比较

Transparent	Pool	Cluster
Contain a single table. Used to store master data	They are used to hold a large number of very small tables(stores customizing       data or system data)	They       are used to hold data from a few number of large tables.(stores system       data)
It       has a one-to-one relationship with a table in the database	It       has a many-to-one relationship with a table in the database	It       has a many-to-one relationship with table in the database
For       each transparent table there is one associated table in the database	It       is stored with other pooled tables in a single table called table pool in       the database	Many       cluster tables are stored in a single table in the database called a table       cluster
The       database table has the same name, same number of fields and the fields       have the same names	The       database table has different name, different number of fields and fields       have different names	The       database table has different name, different number of fields and fields       have different names
There       is only a single table	Table       pools contain more tables than table clusters	Contains       less tables than table pools
Single       table can have one or more primary key	Primary       key of each table does not begin with same fields or fields	Primary       key of each table begins with same fields or fields
Secondary       indexes can be created	Secondary       indexes cannot be created	Secondary       indexes cannot be created
They       can be accessed using open and native SQL	They       can be accessed using open SQL only	They         can be accessed using open  SQL         only
USE:       They are used to hold master data e.g. Table vendors or table of       customers. Example of transaction data is orders placed by customers	USE:       They reduce the amount of database resources needed when many small tables       have to be opened at the same time	USE:       They would be used when the tables have primary key in common and data in       these tables are all accesses simultaneously

• 透明表：创建一个透明表，数据库里面会相应创建一个数据库表并且结构和透明表一致。我们维护该表相当于直接作用于数据库表，我们可以直接操作数据库对它的数据进行增删改查，池表和簇表不能在数据库读取，数据库本身不存在同名的表。 对应的table pool和table curster会在数据库建立一个表，但是该表不能直接在数据库操作，因为它存储了其他表字段值的联合。
• 池表：池表作为一种逻辑表必须assign到一个表池，通常用于存储控制数据。数据库本身不存在同名的表，只会有一个和表池对应的数据库表， 多个池表的数据联合存储在一个表池中。
• 簇表：和池表类似，簇表在定义的时候也必须assign给一个表簇，数据库本身不存在同名的表，只会有一个和表簇对应的数据库表，多个簇表的数据联合存储在一个表簇中。
  

池表和簇表的区别是池表放的数据量相对少，簇表可以放大量数据，但是表池可以拥有很多池表，表簇包含的簇表少。池表的表之间没有关联，簇表表之间要关联。