SAP ITAB KEY SECONDARY documentation, setup help and example usage

ARTICLE

Secondary Table Key
Hash keys and
sorted keys can be declared as
secondary table keys for each internal table. For each sorted key, an additional secondary table index
is created.
Access to an internal table using a secondary key is always optimized. This allows additional optimized keys to be introduced for sorted and hashed tables as well as optimized key accesses for standard tables.

Declaration of Secondary Table Keys

For data types declared in ABAP programs, a secondary table key is declared using additions
UNIQUE|NON-UNIQUE KEY key_name COMPONENTS of statements TYPES , DATA and so on. For table types created in the ABAP Dictionary, the tool provides the corresponding functions.

Access Using Secondary Keys

In key accesses to internal tables, the addition WITH [TABLE] KEY key_name can be used in
processing statements to specify which secondary table key to use. In index accesses, USING KEY keyname can be used to specify the table index of which secondary key to use. In table expressions , this is specified using the addition KEY . Secondary keys are not selected automatically. If no secondary key is specified in a processing statement, the primary key or primary table index is always used. If no explicit key is specified for a table expression, a free search key is used to perform reads.
Statements where secondary keys can be specified are:

READ TABLE itab

The rows to be read can be specified using a secondary key.

LOOP AT itab

The processing sequence and conditions can be controlled using a secondary table key.

INSERT itab

Only a secondary key for the source table can be specified here, from which multiple rows are copied. The position they are inserted at is determined solely using the primary key and the primary index.

APPEND

Only a secondary key for the source table can be specified here, onto which multiple rows are appended.

MODIFY itab

The rows to be modified can be specified using a secondary key.

DELETE itab

The rows to be deleted can be specified using a secondary key.
If the system field sy-tabix is set by this type of access, and a sorted secondary key is used, the row number refers to the associated secondary table index . In statements that these additions has not been introduced for, like SORT , COLLECT , or PROVIDE , secondary keys are not explicitly supported.
The key fields of a secondary table key are only write-protected if the secondary table key is in use in a LOOP loop or in a MODIFY
statement. Otherwise, the secondary key fields are not write-protected.
ABAP_PGL Secondary Keys

Notes

Optimized access times for the individual rows via secondary keys are bought in exchange for the fact that the ABAP runtime environment then needs to administer the additional keys. For hash keys, this means additional hash administration. For each sorted key, it means an additional secondary table index .

When working with internal tables for which a secondary key is declared, it must be ensured that the required key or table index is used in the processing statements.

Example
Program DEMO_SECONDARY_KEYS demonstrates the specification of a secondary table key and the resulting performance gain.

Other Topics

Updating Secondary Keys

Using Secondary Keys

Restrictions for Secondary Keys

Documentation extract taken from SAP system, � Copyright SAP AG. All rights reserved