Types of Internal Table
1.
Standard Table.
2.
Sorted Table.
3.
Hashed Table.
Standard Tables
The
most appropriate type if one is going to address the individual table entries
using the index or key. Index access is the quickest possible access. Standard
tables have an internal linear index. The indexes of internal tables are
administered as trees.
If you
need key access, standard tables are particularly useful if you can fill and
process the table in separate steps. Key access
to a standard table uses a linear search. The response time for key
access is proportional to the number of entries in the table. The key of a
standard table is always non-unique. If no key is specified, the standard table receives the default
key, which is a combination of all character-like fields.
You
cannot specify a unique key. This means that standard tables can always be
filled very quickly, since the system does not have to check whether there are
already existing entries. This means that standard tables can always be filled
very quickly, since the system does not have to check whether there are already
existing entries.
Sorted Tables
The
most appropriate type if you need a table which is sorted as you fill it. You
fill sorted tables using the INSERT statement. Entries are inserted according to
the sort sequence defined through the table key. Any illegal entries are
recognized as soon as you try to add them to the table. The response time for
key access is logarithmically proportional to the number of table entries,
since the system always uses a binary search. Sorted tables are particularly
useful for partially sequential processing in a LOOP if you specify the
beginning of the table key in the WHERE condition.
If the key is not unique, the system takes the entry with the
lowest index. Sorted tables are always saved sorted by the key. They also have an
internal index. The system can access records either by using the table index
or the key. The response time for key access is logarithmically proportional to
the number of table entries, since the system uses a binary search. The key of
a sorted table can be either unique or non-unique. When you define the table,
you must specify whether the key is to be unique or not.
Hashed Tables
The
most appropriate type for any table where the main operation is key access. You
cannot access a hashed table using its index. The response time for key access
remains constant, regardless of the number of table entries. Like database
tables, hashed tables always have a unique key. Hashed tables are useful if you
want to construct and use an internal table which resembles a database table or
for processing large amounts of data.
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 or INSERT itab within a LOOP)
are not allowed. Hashed tables have no linear index. The key of hashed tables must be unique.
Index Tables
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 also referred to as index tables because both
tables can be accessed using the table index. Standard tables and sorted tables are known generically as index tables.
Standard tables and sorted tables are also referred to as index tables because both
tables can be accessed using the table index. Standard tables and sorted tables are known generically as index tables.
