ABAP_SYNTAX DEFINE FILTER DEPENDENCY RULE drul ON dbtab IF { cond_pattern } THEN { derived_cond }
What does it do? Variant of the Dictionary DDL statement DEFINE DEPENDENCY RULE used to define a filter dependency rule . A filter dependency rule can be defined for exactly one DDIC database table dbtab. It derives an additional filter condition derived_cond from the pattern cond_pattern. When the DDIC database table is read, the SAP HANA database optimizer finds the pattern in the WHERE condition and, if necessary, adds the additional filter condition AND to this condition. cond_pattern In cond_pattern, a pattern from a relational expression can be specified in the curly brackets after IF as follows: lhs =$| < $|>$| < =$|>= rhs It is not possible to join multiple expressions using AND or OR or to negate them using NOT.
The following can be specified as the left side lhs of the comparison:
dbtab.column for a column column of the DDIC database table dbtab.
The following can be specified as the right side rhs of the comparison:
dbtab.column for a column column of the DDIC database table dbtab.
An untyped character literal or an untyped numeric literal. This syntax is the same as in untyped literals in ABAP CDS.
A numbered placeholder $1, $2, ... derived_cond In derived_cond, a template from a relational expression can be specified in the curly brackets after THEN as follows: lhs =$| < $|>$| < =$|>= rhs $[OR lhs =$| < $|>$|<(> <<)>=$|>= rhs ...$] Single comparisons can be placed in parentheses ( ). Negations using NOT are not possible.
The following can be specified as the left side lhs of a comparison:
dbtab.column for the column column of the database table dbtab.
The following can be specified as the right side rhs of a comparison:
dbtab.column for the column column of the database table dbtab.
An untyped character literal or an untyped numeric literal. This syntax is the same as in untyped literals in ABAP CDS .
A numbered placeholder $1, $2, ..., which must also be specified in cond_pattern. When the condition is added, the operand for the condition is inserted into this placeholder. The same placeholder for the same operand value must exist in the pattern cond_pattern .
Built-in functions in ABAP Dictionary in ABAP CDS syntax.
Simple case distinctions in ABAP CDS syntax.
Latest notes:
It cannot be guaranteed that the SAP HANA database optimizer finds the pattern cond_pattern. This is why the additional condition derived_cond must not modify the result set of the original query. It is technically possible to modify the result set with a dependency rule, but produces undefined behavior in cases where the SAP HANA database optimizer finds the pattern cond_pattern in some reads but not in others.
The additional condition for a query can be viewed in the SQL Trace tool (transaction ST05) by choosing Display Execution Plan . ABAP_HINT_END
Example ABAP Coding
The following dependency rule demonstrates how the additional condition works: DEFINE FILTER DEPENDENCY RULE demo_drul_1 ON demo_parts_1 IF { demo_parts_1.value > $1 } THEN { demo_parts_1.area = $1 } On the SAP HANA database, this dependency rule modifies the result set of every read performed on the DDIC database table DEMO_PARTS_1. This is done for demonstration purposes here and should never occur in real situations. The program DEMO_DEPENDENCY_RULE_1 uses identical SELECT statements to access the DDIC database table DEMO_PARTS_1 with a dependency rule and an identical table, DEMO_PARTS, without a dependency rule: DATA num TYPE i. cl_demo_input=>request( CHANGING field = num ). 'Dependency Rule demo_drul_1 SELECT * FROM demo_parts_1 WHERE value > @num ORDER BY id INTO TABLE @DATA(result1). cl_demo_output=>write( result1 ). 'No Dependency Rule SELECT * FROM demo_parts WHERE value > @num ORDER BY id INTO TABLE @DATA(result2). cl_demo_output=>display( result2 ). When DEMO_PARTS_1 is accessed, the SAP HANA database optimizer evaluates the dependency rule. It finds the pattern demo_parts_1.value > $1 and adds the additional condition accordingly to create the following logical condition: WHERE value > @num AND area = @num. This restricts the result set to those rows in which the column AREA also has the value of num. This restriction does not apply when DEMO_PARTS is accessed. If the first SELECT statement is transformed into a WITH statement or if alias names are used, for example, the optimizer may not find the pattern and may not add an additional condition. Therefore, the result of this example is dependent on the behavior of the optimizer, which should never occur in production programs. ABAP_EXAMPLE_END
Example ABAP Coding
The following filter dependency rule for the DDIC database table DEMO_PARTS_2 should not modify the result set. For this to happen, the data in the DDIC database table must have the expected values. DEFINE FILTER DEPENDENCY RULE demo_drul_2 ON demo_parts_2 IF { demo_parts_2.value >= 30 } THEN { demo_parts_2.area >= 3 } The program DEMO_DEPENDENCY_RULE_2 uses identical SELECT statements to access the DDIC database table DEMO_PARTS_2 with a dependency rule and an identical table, DEMO_PARTS, without a dependency rule: 'Dependency Rule demo_drul_2 SELECT * FROM demo_parts_2 WHERE value >= 30 AND value < 40 ORDER BY id INTO TABLE @DATA(result1). 'No Dependency Rule SELECT * FROM demo_parts WHERE value >= 30 AND value < 40 ORDER BY id INTO TABLE @DATA(result2). ASSERT result1 = result2. If the data in the DDIC database table is structured so that in rows where the column VALUE contains values greater than or equal to 30 and the values in the column AREA are greater than or equal to 3, the result sets of both reads are identical. To derive an additional condition with a dependency on the condition value <(> <<)> 40, a further filter dependency rule could be defined for the same DDIC database table. ABAP_EXAMPLE_END
