ABAP CDS - SELECT, element - ABAP Keyword Documentation

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ABAP CDS - SELECT, element

Syntax

... { [@element_annot1]
      [@element_annot2]
      ...
        [KEY] { { field
                | path_expr [AS alias] }
              | { literal
                | parameter
                | session_variable
                | aggr_expr
                | arith_expr
                | builtin_func
                | case_expr
                | cast_expr AS alias }
    [@<element_annot1]
      [@<element_annot2]
      ... }
  | { $EXTENSION.* } }  ...

Alternatives:

1. ... field|path_expr|literal|parameter|...

2. ... $EXTENSION.*

Effect

Defines an element of a SELECT list of a CDS view. The names of the elements of a SELECT list must be unique.

Alternative 1

... field|path_expr|literal|parameter|...

Extras:

1. ... @element_annot ... @<element_annot

2. ... KEY

3. ... AS alias

Effect

Specifies individual elements.

When the name field is specified directly, an element of a data source data_source of the current CDS view is defined as an element. The field name can be prefixed with the name of the data source or its alternative name. The prefix is separated using a period (.). AS can be used to define an alternative element name alias.

When a path expression path_expr is specified, two cases arise:

If the path expression identifies an element, the target of the path expression is defined as an element. The element is part of the results set of the CDS view, a field of the CDS database view, and a component of a type defined in ABAP with respect to the CDS view. If no alternative element name alias is defined, and there is no name list, the element name is defined by the name of the element named by the path expression.

If a path expression is specified that ends with an association, this association is published for use in other CDS views or in Open SQL. A different CDS view can evaluate the association in its path expressions. In the same way, the association can be used in path expressions in Open SQL. Like every element, an association published in this way is part of the SELECT list and must also be specified in a name list. It is not, however, part of the results set, a field of the CDS database view of the CDS view, or a component of a type defined in ABAP with respect to the CDS view. If no alternative element name alias is defined, and there is no name list, the element name is defined by the name of the association named by the path expression.

AS can be used to define an alternative element name alias.

literal can be used to declare a literal. AS must be used to define an alternative element name alias. The literal can be prefixed with the name of a domain.

parameter can be used to specify a parameter from the parameter list parameter_list. If AS is used, an alternative element name alias must be defined, which cannot be the name pname of the parameter.

session_variable can be used to specify a session variable. AS must be used to define an alternative element name alias.

Mit aggr_expr, arith_expr, builtin_func and case_exp can be used to specify aggregate expressions, arithmetic expressions, calls of predefined functions in the database, and case distinctions. The expressions and functions are evaluated when the CDS view is accessed in the database system. If AS is used, an alternative element name alias has to be defined, unless there is a name list.

If an association is published in the SELECT list using a path expression path_expr, all fields of the source data source that occur in the ON condition must also be specified as elements of the SELECT list. If a path expression contains more than one association, this type of element must be listed as a path expression closed by the field.

Notes

When publishing an association using a path expression path_expr in the SELECT list, it is not possible to pass actual parameters to any input parameters of the target data source to assign start values to the input parameters.

That the names of the elements of a SELECT list have to be unique applies in particular also for the publication of an association using the path expression path_expr. There must be not other element with this name. If necessary, AS must be used to define an alternative element name alias for the association.

An association can be published multiple times with various alternative element names. This allows you to use different filter conditions cond_expr.

Special rules apply to the publication of associations in SELECT statements joined with UNION.

Example

The following CDS view opens its own association _spfli and the association _sflight published by its target data source demo_cds_assoc_spfli. The fields of the source data source, which are used in the ON conditions of the associations, are specified in the SELECT list. In the case of the association published using _spfli._sflight, path expressions _spfli.carrid and _spfli.connid must be used accordingly. The element scarr occurs twice, which means that an alternative element name must be defined using AS.

@AbapCatalog.sqlViewName: 'DEMO_CDS_PUBASC'
@AccessControl.authorizationCheck: #NOT_REQUIRED
define view demo_cds_publish_assoc
  as select from
    scarr
    association to demo_cds_assoc_spfli as _spfli on
      scarr.carrid = _spfli.carrid
    {
      _spfli,
      scarr.carrid as scarr_carrid,
      _spfli._sflight,
      _spfli.carrid,
      _spfli.connid
    }

Addition 1

... @element_annot ... @<element_annot

Effect

Specifies annotations for the element. The annotations can be specified before the element using @element_annot or after the element using @<element_annot.

Note

An annotation can be used to assign further technical and semantic attributes to an element in ABAP Dictionary. Framework-specific annotations can be used to give the element specific semantic attributes for other SAP frameworks.

Addition 2

... KEY

Effect

KEY is used to define the current element as the key element of the current CDS entity. Any elements of a SELECT list can be defined as key elements that are placed without gaps at the start of the list.

The key elements of the CDS entity are evaluated as follows if they are used as a data source of a SELECT statement in Open SQL.

By the addition ORDER BY PRIMARY KEY.

In implicit access control.

By default, the key elements of the CDS entity are used to document the semantics of the data model. The addition KEY is then ignored when the CDS view is activated and when other accesses are performed in program executions.

The default setting can be overridden using the view annotation AbapCatalog.preserveKey:

If the value true is specified for this annotation, the key elements defined using KEY are also used as keys of the CDS database view.

If this annotation is not specified or specified with the value false, the key elements defined using KEY are ignored by the key of the CDS database view. Like in classic views, the key fields of the database view are derived implicitly from the key fields of the basis tables and the join conditions. If this is not possible, all fields of the database view are key fields.

Notes

In SAP buffering, the key fields of the CDS database view are always the decisive key fields.

In the syntax check in Open SQL, the key elements used depend on whether the name of the CDS entity is specified or the CDS database view (with the latter being obsolete).

Addition 3

... AS alias

Effect

Defines an alternative element name for the current element. The alternative element name replaces the actual name of the element from the data source data_source. The view field is created under the alternative element name in the CDS database view. Accordingly, the alternative element name must comply with the rules for names of view fields of database views, as well as the general naming rules for names:

which means that it must also meet the

naming conventions for component names of structures in ABAP Dictionary and

cannot be a reserved component name. The reserved names that cannot be used are in the database table TRESE.

This is only checked, however, if there is no explicit name list that overrides the alternative element names.

Alternative element names can be used in the current CDS view to grant unique names for identically named elements from different entities of the data source. When the current CDS view is accessed, the alternative element names must be used instead of the actual name. Alternative element names cannot be used within the CDS view, with one exception: alternative element names can be specified directly or after $projection in the ON condition of an association.

Alternative 2

... $EXTENSION.*

Effect

Specifies all elements of an enhancement of the enhancement concept for classic objects in ABAP Dictionary. If $EXTENSION.* is specified as an element, all fields that occur in an enhancement of a database table or a classic view in ABAP Dictionary in the data source data_source become elements of the current CDS view automatically.

If $EXTENSION.* is specified, it works only for the current CDS view. It is not applied to other CDS views in whose data source the current CDS view is used or to CDS views in the data source of the current CDS view.

$EXTENSION.* cannot be specified if aggregate expressions aggr_expr occur in the current SELECT list or if the current CDS view is a union set created using UNION.

Notes

$EXTENSION.* is specified independently of when an enhancement is made. It is also applied when a database table or a view is enhanced only after the activation of the CDS view.

The statement EXTEND VIEW can be used to enhance the current CDS view.

Example

The data source of the CDS view sales_order is an inner join of the database tables snwd_bpa and snwd_so and contains three directly defined elements sales_order_id, business_partner_id, and company_name and (because $EXTENSION.* is specified) all fields that exist due to enhancements in the database tables snwd_bpa and snwd_so. The alternative name partner is defined for the database snwd_bpa and is used in the ON condition. The names of the elements sales_order_id and business_partner_id are alternative element names. The element sales_order_id is defined as a key element.

@AbapCatalog.sqlViewName: 'SALES_ORDER_VW'
define view sales_order as
  select from snwd_bpa as partner
    inner join
      snwd_so on partner.node_key = snwd_so.buyer_guid
  { key so_id as sales_order_id,
        bp_id as business_partner_id,
        company_name, //from snwd_bpa
        $extension.* }

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ABAP CDS - SELECT, element_annot