Tables are the important and mainly used data dictionary object. It is defined independently of the RDBMS. Each field of the table should be defined with its data type and length (or can populate this with using an activated domain).Normally a table definition consists of fields, foreign keys, technical settings and indexes.
In SAP data dictionary there are mainly three types of tables are there.
- Transparent tables
- Pooled tables
- Cluster tables
These types of tables have a one-to-one relationship with tables in RDBMS. For each transparent table there will be corresponding table in real database. These are the most commonly used tables we are dealing with. They are used for storing the application data (master data or transaction data in an application).
These types of tables have a many-to-one relationship with tables in RDBMS. It means for a single table in RDBMS there will be several tables in data dictionary. In database a special type of table called Table pool will contain all these pooled tables. It mainly consists of a large number of very small tables. It will reduce the database resource to avoid open several small tables at a time. It mainly used for storing the customizing data in SAP.
It is almost similar to pooled tables with many-to-one relationship with tables in RDBMS. Like Table pool the Table cluster consists of the cluster tables in database. It mainly consists of a few numbers of large tables (this is the main difference with Table pool). Second difference with table pool and table cluster is the cluster tables will begin with a common primary field (or fields).So the database resource using while opening several tables with a common primary key can be avoided using a table cluster.