ARTICLE
Primary Table Key
Each internal table has a primary table key that enables access to
individual rows in the table by means of a key specification.
The components of the primary table key are declared using the
UNIQUE|NON-UNIQUE KEY additions of
the statements TYPES ,
DATA , and so on.
The standard key , which can be declared
both explicitly and implicitly, has a special part to play here.
The primary table key of a standard table
can also be empty , meaning that it does
not contain any key fields.
In the case of key accesses for internal tables, the primary key is
always used implicitly processing
statements as long as no secondary key is specified. In
table expressions , the primary key must
also always be specified explicitly.
The primary key has the predefined name primary_key , with which
it can also be addressed explicitly in processing statements. In table
expressions, primary_key or an alias name must be specified, if
the primary key is to be used explicitly.
Access to an internal table using the primary table key is determined by
the table type and not the table key.
For sorted tables and hashed tables, key access is always optimized
using the primary table key. Primary key access to standard tables,
however, uses a linear search.
The key fields of the primary table key of sorted tables and hashed
tables are always read-only.
In the case of sorted tables and hashed tables, separate key
administration exists for the primary table key, which enables optimized
access but also affects the memory requirement
of the internal table. There is no separate key administration for
the primary table key of standard tables.
Notes
Since sorted tables and hashed tables have real key administration for
the primary key, unlike standard tables, these tables are also grouped
under the term key tables .
To achieve optimized key access to standard tables,
secondary keys can be used.
Documentation extract taken from SAP system, � Copyright SAP AG. All rights reserved
