topic Database tables in Application Development and Automation Discussions

Database tables

Former Member — Wed, 06 Jun 2007 14:02:35 GMT

What is the diff b/w POOLED TABLES and CLUSTER TABLES?

Re: Database tables

Former Member — Thu, 07 Jun 2007 04:19:21 GMT

Hi Narsaiah,

Transparent Table:

Exists with the same structure both in dictionary as well as in database exactly with the same data and fields.

Pooled Table:

Pooled tables are logical tables that must be assigned to a table pool when they are defined. Pooled tables are used to store control data. Several pooled tables can be cominied in a table pool. The data of these pooled tables are then sorted in a common table in the database.

Cluster Table:

Cluster tables are logical tables that must be assigned to a table cluster when they are defined. Cluster tables can be used to strore control data. They can also be used to store temporary data or texts, such as documentation.

A transparent table is a table that stores data directly. You can read these tables directly on the database from outside SAP with for instance an SQL statement.

Transparent table is a one to one relation table i.e. when you create one transparent table then exactly same table will create in data base and if is basically used to store transaction data.

A clustered and a pooled table cannot be read from outside SAP because certain data are clustered and pooled in one field.

One of the possible reasons is for instance that their content can be variable in length and build up. Database manipulations in Abap are limited as well.

But pool and cluster table is a many to one relationship table. This means many pool table store in a database table which is know as table pool.

All the pool table stored table in table pool does not need to have any foreign key relationship but in the case of cluster table it is must. And pool and cluster table is basically use to store application data.

Table pool can contain 10 to 1000 small pool table which has 10 to 100 records. But cluster table can contain very big but few (1 to 10) cluster table.

For pool and cluster table you can create secondary index and you can use select distinct, group for pool and cluster table. You can use native SQL statement for pool and cluster table.

A structure is a table without data. It is only filled by program logic at the moment it is needed starting from tables.

A view is a way of looking at the contents of tables. It only contains the combination of the tables at the basis and the way the data needs to be represented. You actually call directly upon the underlying tables.

http://www.datamanagementgroup.com/Resources/Articles/Article_0106_2.asp

more info

http://help.sap.com/saphelp_erp2004/helpdata/en/81/415d363640933fe10000009b38f839/frameset.htm

http://cma.zdnet.com/book/abap/ch03/ch03.htm

Check this links.

http://help.sap.com/saphelp_40b/helpdata/en/4f/991f82446d11d189700000e8322d00/applet.htm

http://www.techinterviews.com/?p=198

reward pts if usefull

Regards

Sathish

Re: Database tables

former_member196299 — Thu, 07 Jun 2007 04:34:49 GMT

hi ,

Here you go with the difference :

Check this link :

http://help.sap.com/saphelp_nw04/helpdata/en/81/415d363640933fe10000009b38f839/frameset.htm

Reward for all helpful answers !

Regards,

Ranjita

Re: Database tables

anversha_s — Thu, 07 Jun 2007 04:36:10 GMT

hi,

Pooled table

A pooled table in R/3 has a many-to-one relationship with a table in the database.

For one table in the database, there are many tables in the R/3 Data Dictionary.

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.

When you look at a pooled table in R/3, you see a description of a table.

However, in the database, it is stored along with other pooled tables in a single table called a table pool.

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). Table pools reduce the amount of database resources needed when many small tables have to be open at the same time. SAP uses them for system data. You might create a table pool if you need to create hundreds of small tables that each hold only a few rows of data. To implement these small tables as pooled tables, you first create the definition of a table pool in R/3 to hold them all. When activated, an associated single table (the table pool) will be created in the database. You can then define pooled tables within R/3 and assign them all to your table pool.Pooled tables are primarily used by SAP to hold customizing data.

Cluster Table

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.

Like pooled tables, cluster tables are another proprietary SAP construct.

They are used to hold data from a few (approximately 2 to 10) very large tables.

They would be used when these tables have a part of their primary keys in common,

and if the data in these tables are all accessed simultaneously. The data is stored logically.

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.

A cluster is advantageous in the case where data is accessed from multiple tables simultaneously

and those tables have at least one of their primary key fields in common.

Cluster tables reduce the number of database reads and thereby improve performance.

Restrictions on Pooled and Cluster Tables

Pooled and cluster tables are usually used only by SAP and not used by customers,

probably because of the proprietary format of these tables within the database

and because of technical restrictions placed upon their use within ABAP/4 programs.

On a pooled or cluster table:

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.

Regards

Anversha

Re: Database tables

Former Member — Thu, 07 Jun 2007 04:48:19 GMT

Hi,

A clustered and a pooled table cannot be read from outside SAP because certain data are clustered and pooled in one field.

One of the possible reasons is for instance that their content can be variable in length and build up. Database manipulations in Abap are limited as well.

But pool and cluster table is a many to one relationship table. This means many pool table store in a database table which is know as table pool.

Table pool can contain 10 to 1000 small pool table which has 10 to 100 records. But cluster table can contain very big but few (1 to 10) cluster table.

For pool and cluster table you can create secondary index and you can use select distinct, group for pool and cluster table. You can use native SQL statement for pool and cluster table.

<b>Pooled Tables :</b>

Different tables which are not linked to each other with a common key can be combined into a Table Pool. The tables contained within this pool are called Pooled Tables. A table pool is stored in the database a simple table. The table's data sets contain, in separate fields, the actual key for the data set to be stored, the name of the pooled table and the contents of the data set to be stored.

Using this schema, several logical tables are combined into a single real database table. Although the data structure of each set is lost during the write to the table pool, it is restored during the read by the ABAP/4 Data Dictionary. The ABAP/4 Data Dictionary utilizes its meta-data to accomplish this.

Since information must be prepared (defined) within the ABAP/4 Data Dictionary when it is read or written to (or accessed), this process itself defines these as not transparent tables.

<b>Cluster Tables :</b>

Occasionally, several tables may be linked by a common key. The ABAP/4 Data Dictionary can also combine these tables into a single table. Each data set of the real table within the database contains a key and in a single data field, several data sets of the subsequent table for this key.

As mentioned above, these table types require special data handling, therefore they are not transparent tables.

Note: Both Pooled and Cluster Tables are stored as tables within the database. Only the structures of the two table types which represent a single logical view of the data are defined within the ABAP/4 Data Dictionary. The data is actually stored in bulk storage in a different structure. These tables are commonly loaded into memory (i.e., 'buffered') due to the fact they are typically used for storing internal control information and other types of data with little or no external (business) relevance.

Here are some really good links

http://help.sap.com/saphelp_nw04/helpdata/en/cf/21f083446011d189700000e8322d00/content.htm

Hope this helps.

Regards,

Richa