ABAP Keyword Documentation → ABAP - Dictionary
Dependency Rules in ABAP Dictionary
A dependency rule is a dictionary object, an instance of which is created on an SAP HANA database. A dependency rule is defined for one or more database tables. From a relational expression of a selection condition, it derives an additional condition for these database tables. The SAP HANA database optimizer evaluates this instruction when the database tables are read. If possible, it creates the additional selection conditions and uses AND to join it with the other conditions.
ABAP Dictionary dependency rules are defined using the
Other versions:
7.31 | 7.40 | 7.54
Caution
It cannot be guaranteed that the SAP HANA database evaluates a dependency rule correctly by creating the required additional selection condition. In queries with common table expressions, alias names, and so on, it can occur that the optimizer does not detect the selection condition in question. For this reason, dependency rules must only be defined in ways that do not modify the results set and that are useful for the internal optimizer. When a database table is accessed by an application program, the result must always be the same, regardless of any dependency rules. This is the only way to avoid producing results that are dependent on the behavior of the optimizer.
Notes
- Dependency rules usually join semantic columns of a database table with technical columns of the same table. Semantic columns contain regular data and technical columns contain data used for internal database processes. ABAP programs should not access the data in technical columns in most cases. A dependency rule can be used to create additional selection conditions from selection conditions for semantic columns. This modifies access to the table in a transparent way for the ABAP program.
- One important application for dependency rules is the optimization of access to old data in database tables where data aging is enabled. In this case, dependency rules join the temperature column of a database table with regular date columns in the table.
- In all SQL reads on database tables, the SAP HANA database optimizer evaluates their dependency rules. This is done regardless of the access type and covers access with ABAP SQL, AMDP, and Native SQL, plus access to views that have a database table of this type as a data source. Dependency rules are not evaluated in reads not made using SQL (such as in calculation views).
- Partners and customers cannot currently define their own dependency rules.