STANDARD table
Key access to a standard table uses a linear search. This means that the time required for a search is in linear relation to the number of table entries.
You should use index operations to access standard tables.
SORTED table
Defines the table as one that is always saved correctly sorted.
Key access to a sorted table uses a binary key. If the key is not unique, the system takes the entry with the lowest index. The runtime required for key access is logarithmically related to the number of table entries.
HASHED table
Defines the table as one that is managed with an internal hash procedure
You can only access a hashed table using the generic key operations or other generic operations ( SORT, LOOP, and so on). Explicit or implicit index operations (such as LOOP ... FROM oe INSERT itab within a LOOP) are not allowed.
INDEX table
A table that can be accessed using an index.
Index table is only used to specify the type of generic parameters in a FORM or FUNCTION. That means that you can't create a table of type INDEX.
Standard tables and sorted tables are index tables.
Syntax :
DATA itab TYPE table type of line type [WITH UNIQUE/NON-UNIQUE KEY <key>] [Iinitial size n] [WITH HEADER LINE]
What are DATA CLUSTERS ?
You can group any complex internal data objects of an ABAP/4 program together in data clusters and store them temporarily in ABAP/4 memory or for longer periods in databases. You can store data clusters in special databases of the ABAP/4 Dictionary. These databases are known as ABAP/4 cluster databases and have a predefined structure.Storing a data cluster is specific to ABAP/4. Although you can also access cluster databases using SQL statements, only ABAP/4 statements are able to decode the structure of the stored data cluster.
