Enhancement of SAP Standard Tables

Append structures allow you to append fields to standard SAP tables and structures without modifying the table definition.

An append structure is a structure that is assigned to exactly one table. There can be several append structures for a table.

When a table is activated, all the active append structures for the table are found and their fields are appended to the table. If an append structure is created or changed, the table to which it is assigned is also activated.

Like all structures, an append structure defines a type that can be used in ABAP programs.

As of Release 4.6C, you can define foreign keys for fields that already exist in the table using an append structure. Search helps can also be attached to fields that already exist in the table.​

Hint: If you copy a transparent table in the ABAP Dictionary to which an append structure has been added, the fields of the append structure are converted to normal table fields.

Customers create append structures in their namespace. The append structures are thus protected against overwriting during an upgrade.

The new versions of the standard tables are imported during the upgrade. When the standard tables are activated, the fields contained in the active append structures are appended to the new standard tables. When append structures are added to a table, you do not have to manually adjust the customer modifications to the new SAP version of the table (transaction SPDD) during the upgrade.

As the order of the fields in the ABAP Dictionary can differ from the order on the database, a conversion is not necessary when you add an append structure or insert fields in an existing append structure. The structure is adjusted when the database catalog is adjusted (ALTER TABLE). When you activate a structure in the ABAP Dictionary, the definition of the table is changed and the new field is appended to the database table.

Caution: Note the following restrictions regarding append structures:

• No append structures may be created for pooled and cluster tables.
• Tables containing a long field (data type LCHR or LRAW) cannot be extended with appends structures. This extension is not possible because long fields have to be the last field of the table.
• The fields in the append structure must be in the customer namespace beginning with YY or ZZ. Using the customer namespace prevents name conflicts with future table fields delivered by SAP.
• If, as a partner, you have your own reserved namespace, it is recommended that you choose the names for your append structures from your namespace.

Enhancement of Tables

Structures and tables that have been defined by SAP in the ABAP Dictionary can be enhanced by the customer in the following ways:

• Customizing includes
  With this variant, certain places within a standard structure or table are reserved by SAP for customer enhancements. The Customizing environment supports customers using these Customizing includes.

 

• Using appends
  With this variant, any fields without previous reservation are appended to the end of structures or tables.

Caution: Enhancements using append structures may cause the following problems:

• Structure enhancements affect not only the enhanced structure itself, but also all dependent structures that use the enhanced structure as an include or substructure.
  However, when the enhanced structure is included in a dependent structure, this can lead to fields in the dependent structure being displaced. This is the case, for example, when the include appears in the middle of the dependent structure. The field displacement can prevent ABAP programs from reading the structure correctly. 

 

• In programs with de-activated Unicode checks, structure enhancements can lead to syntax and runtime errors.
  These errors are generally found in type checks and in connection with deep structures.

 

• In programs with activated Unicode checks, structure enhancements additionally affect value assignments, operand checks, and accesses with offset and length. For example, numerical or deep components are inserted into a purely character-like structure. Enhancements may also cause some issues because the fragment view is changed, and checks in assignments and comparisons that are based on this are affected as a result.