Types of database tables

Question

types of database tables and one line definition

Answer 1

Hi
Table Types
Standard table:
The key access to a standard table uses a sequential search. The time required for an access is linearly dependent on the number of entries in the internal table.
You should usually access a standard table with index operations.
Sorted table:
The table is always stored internally sorted by its key. Key access to a sorted table can therefore use a binary search. If the key is not unique, the entry with the lowest index is accessed. The time required for an access is logarithmically dependent on the number of entries in the internal table.
Index accesses to sorted tables are also allowed. You should usually access a sorted table using its key.
Hash table:
The table is internally managed with a hash procedure. All the entries must have a unique key. The time required for a key access is constant, that is it does not depend on the number of entries in the internal table.
You cannot access a hash table with an index. Accesses must use generic key operations (SORT, LOOP, etc.).
Index table:
The table can be a standard table or a sorted table.
Index access is allowed to such an index table. Index tables can be used to define the type of generic parameters of a FORM (subroutine) or a function module.
Just have a look at these links:
http://help.sap.com/saphelp_nw04/helpdata/en/90/8d7304b1af11d194f600a0c929b3c3/frameset.htm
http://help.sap.com/saphelp_nw04/helpdata/en/74/83015785d811d295a800a0c929b3c3/frameset.htm
Pooled Tables, Table Pools, Cluster Tables, and Table Clusters
These types of tables are not transparent in the sense that they are not legible or manageable directly using the underlying database system tools. They are managed from within the R/3 environment from the ABAP dictionary and also at runtime when they are loaded into application memory.Pool and cluster tables are logical tables. Physically, these logical tables are arranged as records of transparent tables. The pool and cluster tables are grouped together in other tables, which are of the transparent type. The tables that group together pool tables are known as table pools, or just pools; similarly, table clusters, or just
clusters, are the tables which group cluster tables.Not all operations that can be performed over transparent tables can be executed over pool or cluster tables.
For instance, you can manage these tables using Open SQL calls from ABAP, but not Native SQL.These tables are meant to be buffered and loaded in memory, because they are commonly used for storing internal control information and other types of data with no external (business) relevance. SAP recommends that tables of pool or cluster type be used exclusively for control information such as
program parameters, documentation, and so on. Transaction and application data should be stored in transparent tables.
Table Pools
From the point of view of the underlying DBMS as from the point of view of the ABAP dictionary, a table pool is a transparent table containing a group of pooled tables which, when created, were assigned to this table pool.
Field Type Description
TABNAME CHAR(10) Table name
VARKEY CHAR(n) Maximum key length n =< 110
DATALN INT2(5) Length of the VARDATA record returned
VARDATA RAW(m) Maximum length of the data varies according to DBMS
Table Clusters
Similarly to pooled tables, cluster tables are logical tables which, when created, are assigned to a table cluster. Therefore, a table cluster, or just cluster, groups together several tables of type clusters.Several logical rows from different cluster tables are brought together in a single physical record. The records
from the cluster tables assigned to a cluster are thus stored in a single common table in the database.A cluster contains a transparent cluster key which must be located at the start of the key of all logical cluster tables to be included in the cluster. As well, a cluster contains a long field (VARDATA), which contains the
data of the cluster tables for this key. If the data does not fit into a field, continuation records are created.
Field Type Description
CLKEY1 CHAR(*) First key fields
CLKEY2 CHAR(*) Second key field
CLKEYN CHAR(*) nth key field
PAGENO INT2(5) Number of the next page
TIMESTMP CHAR(14) Time stamp
PAGELG INT2(5) Length of the VARDATA record returned
VARDATA RAW(*) Maximum length of the data section; varies according to database system
Working with Tables
The dictionary includes many functions for working with tables. There are five basic operations you can perform on tables: display, create, delete, modify, copy. Please do not confuse displaying a table with displaying the table entries (table contents). In order to display a table, it must previously exist; otherwise the system will display an error message in the status bar. For the following example, the table TABNA is used. To display this table, from the main dictionary screen, enter the table name in the Object name
input field with the radio button selected next to Tables. Then, click on the Display button at the bottom of the screen, or press the F7 function key, or, alternatively,
select Dictionary object Display from the menu.
In this screen, you can see table information such as
¨ Table type, shown next to the name of the object. In the example, it is a transparent table.
¨ Short text description.
¨ Name of the user who made the last change, and the date of the change.
¨ Master language.
¨ Table status. On the screen, you can see this table is saved and active.
¨ Development class. For information on development classes, refer to Chap. 6.
Delivery class, which sets the maintenance group for the table. It controls how tables will behave during client copy procedures, upgrades, and so forth.¨
Tab. Maint. Allowed flag, which indicates whether you can generate a screen for maintaining table entries.
¨Then, on the lower part of the screen, you can see the table fields with all associated characteristics such as:
¨ Field name.
¨ Key indicator. When set, this field is the primary key, or part of it.
¨ Data element.
¨ Basic data type.
¨ Length.
¨ Check table.
¨ Short text, describing the field.
Additional information about the table can be displayed by selecting the corresponding functions from the menu or directly from the application toolbar, such as keys, indexes, or technical settings
Regards
Sreeni