About pool table??

Question

what for pooled and cluster table used and how to create it???

Answer 1

I. Transparent tables (BKPF, VBAK, VBAP, KNA1, COEP)
·     Allows secondary indexes (SE11->Display Table->Indexes)
·     Can be buffered (SE11->Display Table->technical settings) Heavily updated tables should not be buffered.
II. Pool Tables (match codes, look up tables)
·     Should be accessed via primary key or
·     Should be buffered (SE11->Display Table->technical settings)
·     No secondary indexes
·     Select * is Ok because all columns retrieved anyway
III. Cluster Tables (BSEG,BSEC)
·     Should be accessed via primary key - very fast retrieval otherwise very slow
·     No secondary indexes
·     Select * is Ok because all columns retrieved anyway. Performing an operation on multiple rows is more efficient than single row operations. Therefore you still want to select into an internal table. If many rows are being selected into the internal table, you might still like to retrieve specific columns to cut down on the memory required.
·     Statistical SQL functions (SUM, AVG, MIN, MAX, etc) not supported
·     Can not be buffered
IV. Buffered Tables (includes both Transparent & Pool Tables)
While buffering database tables in program memory (SELECT into internal table) is generally a good idea for performance, it is not always necessary. Some tables are already buffered in memory. These are mostly configuration tables. If a table is already buffered, then a select statement against it is very fast. To determine if a table is buffered, choose the 'technical settings' soft button from the data dictionary display of a table (SE12). Pool tables should all be buffered.
"Major difference betwen Standard tables,Pooled tables and Cluster Tables?
1.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.
2.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.
3.A clustered and a pooled table cannot be read from outside SAP because certain data are clustered and pooled in one field.
4.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.
5.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.
6.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.
7.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.
8.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.
9.A structure is a table without data. It is only filled by program logic at the moment it is needed starting from tables.
10.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.
'The table which store information about Structures and Tables are as follows:
DD02L - table properties
DD02T - table texts
DD03L - field properties
DD03T - field texts
Creating Pooled Tables/Cluster Tables Locate the document in its SAP Library structure
Procedure
   1. In the initial screen of the ABAP Dictionary select object type Table, enter a table name and choose This graphic is explained in the accompanying text Create.
      The field maintenance screen for the table is displayed. Table type Transparent table is set as default.
   2. Make the necessary entries in the Short description and Delivery class fields on the Attributes tab page. Then define the fields of the table.
      Proceed as when Structure link creating a transparent table. Save your entries.
   3. Choose Extras
      ® Change table category.
      A dialog box appears in which you have to select the table type Pooled table or Cluster table.
   4. Choose This graphic is explained in the accompanying textSelect.
      You return to the field maintenance screen for the table. Field Pool/cluster name is displayed on the Attributes tab page in addition to the standard fields.
   5. Enter the name of the
      table pool or table cluster to which you want to assign the pooled table or cluster table in field Pool/cluster name
      Note that the total key length of a pooled table may not exceed the key length of the associated table pool. The key of a cluster table must correspond to the key of the associated table cluster.
   6. Proceed as when creating a transparent table (see
      Structure link Creating Tables). Remember that you cannot create indexes for pooled or cluster tables.
Note
All the attributes of the Structure link technical settings can be maintained for pooled tables and cluster tables. Before you can access these attributes, however, you must convert the table to a transparent table.
Leaving content frame
creating pool/cluster tables
regards,
srinivas
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