In the sap ,there are three kinds of table. I will demostrate it in the detail. They
are Transparent table ,Pooles tabel,Cluster tables.
Transparent table: One to one relation
One table in data dictionary equal to one table in data base.
i. e When u create one transparent tabel in ABAP dictionary one table will be created in Database(Typically Oracle, U can have others also) with same name(Both tabel and fields).
Basically used to hold application data.
EG: EKKO,VBAK etc.
Pooles tabel: Many to one relationship
Many tables in ABAP dictionary equal to one table pool in database. Basically used to hold system data and customization data. One table pool contains large number of pooled tables having data of around 100 records each.
Cluster tables: Many to one relationship
Many tables in ABAP dictionary equal to one table cluster in database. Basically used to hold application data. One table cluster contains few number of cluster tables having data of around large quantities.(In lakhs)
eg:CDPOS, BSEG etc.
Incase of pooled and cluster tables ABAP data dictionary table name and Data base table and field names differs unlike same in case transparent table.
There are some limitations on cluster tables like we can’t use joins on these tables, Select on cluster table is always very slow.
When ever we write query on any cluster table in the table cluster data will be fetced for all the table as data for all the tables in the cluster stores as a single record.
In reality we hardly create pooled and cluster tables.