Transprant table / Pooled table / Cluster table
Transprant tables:
A transparent table in the dictionary has a one-to-one relationship with a table in the database. The database table has the same name, the same number of fields, and the fields have the same names as the R/3 table definition.They are used to hold application data. Application data is the master data or transaction data used by an application.
Pooled Tables:
A pooled table in R/3 has a many-to-one relationship with a table in the database .The table in the database has a different name than the tables in the DDIC, it has a different number of fields, and the fields have different names as well. Pooled tables are an SAP proprietary construct.
Pooled and cluster tables are not usually used to hold application data but instead hold system data, such as system configuration information, or historical and statistical data.
A table pool is a database table with a special structure that enables the data of many R/3 tables to be stored within it. It can only hold pooled tables. R/3 uses table pools to hold a large number (tens to thousands) of very small tables (about 10 to 100 rows each).
Cluster Tables:
A cluster table is similar to a pooled table. It has a many-to-one relationship with a table in the database. Many cluster tables are stored in a single table in the database called a table cluster.
A table cluster is similar to a table pool. It holds many tables within it. The tables it holds are all cluster tables.
Table clusters contain fewer tables than table pools and, unlike table pools, the primary key of each table within the table cluster begins with the same field or fields. Rows from the cluster tables are combined into a single row in the table cluster. The rows are combined based on the part of the primary key they have in common. Thus, when a row is read from any one of the tables in the cluster, all related rows in all cluster tables are also retrieved, but only a single I/O is needed.
Restrictions on Pooled and Cluster Tables :
Secondary indexes cannot be created.
You cannot use the ABAP/4 constructs select distinct or group by.
You cannot use native SQL.
A transparent table in the dictionary has a one-to-one relationship with a table in the database. The database table has the same name, the same number of fields, and the fields have the same names as the R/3 table definition.They are used to hold application data. Application data is the master data or transaction data used by an application.
Pooled Tables:
A pooled table in R/3 has a many-to-one relationship with a table in the database .The table in the database has a different name than the tables in the DDIC, it has a different number of fields, and the fields have different names as well. Pooled tables are an SAP proprietary construct.
Pooled and cluster tables are not usually used to hold application data but instead hold system data, such as system configuration information, or historical and statistical data.
A table pool is a database table with a special structure that enables the data of many R/3 tables to be stored within it. It can only hold pooled tables. R/3 uses table pools to hold a large number (tens to thousands) of very small tables (about 10 to 100 rows each).
Cluster Tables:
A cluster table is similar to a pooled table. It has a many-to-one relationship with a table in the database. Many cluster tables are stored in a single table in the database called a table cluster.
A table cluster is similar to a table pool. It holds many tables within it. The tables it holds are all cluster tables.
Table clusters contain fewer tables than table pools and, unlike table pools, the primary key of each table within the table cluster begins with the same field or fields. Rows from the cluster tables are combined into a single row in the table cluster. The rows are combined based on the part of the primary key they have in common. Thus, when a row is read from any one of the tables in the cluster, all related rows in all cluster tables are also retrieved, but only a single I/O is needed.
Restrictions on Pooled and Cluster Tables :
Secondary indexes cannot be created.
You cannot use the ABAP/4 constructs select distinct or group by.
You cannot use native SQL.
You cannot specify field names after the order by clause. order by primary key is the only permitted variation.
From : SDN