Course 11 - DB Lookup Expression скачать в хорошем качестве

Course 11 - DB Lookup Expression

he DB lookup expression performs a database lookup from within BRFplus. It is used to access the records stored in a data dictionary (DDIC) table or to retrieve information about a table. Features Modes of Operation Data Retrieval Mode In this mode, the data is retrieved from a database table. The expression performs a simple selection operation in the specified table. The selection is defined by the following settings: Table Name Specifies the database table from which data is read. You can access any table available in the data dictionary of the backend system. It is not necessary to bind the database table to a BRFplus table data object. Field Conditions Specifies the conditions applied to the different table fields for refining the search result. Based on the field conditions, the WHERE clause of the performed selection is built. The value that is actually selected from the table depends on the result data object type: If the result data object is an element with a name corresponding to one of the table fields, the expression only selects that one value. If the result data object is a structure, then the database fields corresponding to the structure fields are read. If the result data object is a table, then the source table fields corresponding to the result table fields are read. As opposed to using an elementary or structure data object, multiple entries can be read. Aggregation Mode In this mode, the result of an aggregation function applied to a database table is returned. The following aggregation functions are supported: Maximum Minimum Sum Average Count The aggregation functions can be applied on distinct fields or on entire table records (all fields in a row). The following example illustrates the effects of changing this setting: Field Mapping When you are working with a DB lookup expression in data retrieval mode, this means that you want to collect a particular subset of records from the database table used as the context data object, and that you want to transfer the selected records into a BRFplus table data object used as the expression's result data object. Generally, the two table data objects involved are not identical (because otherwise, you would overwrite the original table content with the result of the selection). As a consequence, you need to define a mapping relationship between the fields from the source table to the fields in the target table. The maximum number of possible relationships is determined by the number of fields available in the target table. To define the field mapping, you can use the following features: Automatic mapping As soon as you have defined both the source and the target table, the system automatically scans the source table for fields with the same name and type as the fields in the target table. Each matching source field is assigned to the corresponding target field. If you are familiar with the ABAP programming language, you may already know this mechanism that is available with the MOVE-CORRESPONDING statement. The automatic field mapping is just a proposal and can be overwritten manually. Manual mapping You can manually associate source fields to the target fields. This is useful to map fields that have the same semantic but different names, so that the automatic mapping mechanism cannot recognize their correspondence. You can also manually choose from the source fields for already existing automatic mappings. For manual mapping, the system offers you the list of source fields in a menu. However, this menu is restricted to the first nine fields of the table. If the source table contains more fields, you can access these fields by choosing Select other element from the menu. Field aggregation and grouping