SAP CDS UNION V1

Get Example source ABAP code based on a different SAP table

• UNION ABAP_CDS_SELECT_V1
• ALL ABAP_CDS_SELECT_V1

ABAP_CDS_DDL - DDIC-Based View, SELECT, UNION

ABAP_SYNTAX
... UNION $[ALL$] select_statement ...

What does it do?
Merges the rows of the result sets of two SELECT statements of ABAP_CDS_V1_VIEWS into one result set. As a prerequisite, the result sets must have the same number of elements and the element pairs that occur in the same position of the result set must have a compatible data type. The data types DF16_..., DF34_..., LCHR ,LRAW,STRING, RAWSTRING , and GEOM_EWKB are not supported. A union result set can itself be the left side of a further union.
If the addition ALL is specified, all entries, even duplicates, are listed in the result set. If ALL is not specified, all duplicate entries are removed from the result set. For determining the duplicate rows, all columns of the result set are considered. In detail, this works as follows:

First, all rows of all UNION branches are combined into one result set.

Then, all rows that occur more than once (considering all columns, not just key fields) are deleted except for one.
The properties of the elements of the merged result set are determined as follows:

Element names

If an explicit name list is specified, this list determines the names of the elements

If no explicit name list is specified, the direct element names or the alternative element names defined using AS must match for each column in the SELECT lists of all SELECT statements and are used.

Key elements The SELECT list of the first SELECT statement determines the key elements.

Element annotations Only the element annotations from the SELECT list of the first SELECT statement are applied.

Data type

The SELECT list of the first SELECT statement determines the data type of each element of the CDS entity.

The data type used to create the union set on the database is a data type whose value range covers the data types of the associated columns of all result sets involved.
The following table shows which data types can be merged with each other in a union. On the left side, the data types of the SELECT list of the first SELECT statement are listed and the other columns specify with which data types of the following SELECT lists they can be merged. First/followingINT1INT2 INT4INT8DECCURR QUANFLTPCHAR SSTRINGNUMCDATSTIMS ACCPCLNTLANG UNITCUKYRAW
INT1xwwwwwww---------- -
INT2xxwwwwww---------- -
INT4xxxwwwww---------- -
INT8xxxxwwww---------- -
DECwwwwwwww---------- -
CURRwwwwwwww---------- -
QUANwwwwwwww---------- -
FLTPxxxwwwwx---------- -
CHAR--------wwlwwlllll -
SSTRING--------ww------- --
NUMC--------w-llllll-- -
DATS--------w-lx------ -
TIMS--------w-l-x----- -
ACCP--------l-l--x---- -
CLNT--------l-l---x--- -
LANG--------l-l----x-- -
UNIT--------l-------x- -
CUKY--------l--------x -
RAW------------------ x
There are no further restrictions to note in combinations using x . The following rules apply to the other combinations:

In combinations with w, the length or the value range of the data type in the first SELECT must be long enough for all following SELECT lists. If this is not the case, a syntax check warning is raised.

In combinations using l, the lengths of the data types must match exactly.
If the length or value range of the first element does not cover the following elements in combinations with w, the value returned by the database can be too great for the data type of the element of the CDS entity. It is still possible to activate the view here, but the content may be truncated or exceptions may be raised in AB_SQL queries if a type reference is applied to the entity. This is due to the assignment rules of the INTO clause. Assignments to ABAP data objects with a sufficiently large value range, on the other hand, do not cause problems.
A CDS view in which union sets are formed with UNION can expose CDS associations. Such an association must be defined and exposed in the same way in all SELECT statements merged with UNION. That is, CDS associations that are exposed in the respective SELECT lists must appear in all SELECT statements merged with UNION and the following requirements must be met:

They have the same name.

They have the same cardinality.

They must be exposed at the same position in the SELECT list using a path expression.

They must have the same ON conditions, that is:

The conditions must relate to the same fields in the association source and association target and express the same logic for these fields.

The fields of the association source that are listed in an ON condition must be at identical positions in the SELECT list.
These rules also apply if a CDS association is defined in a data source of a SELECT statement and is exposed by the current statement. From outside, the CDS associations with the same name that are exposed in the individual SELECT lists act like a CDS association exposed by the union set. There are no restrictions on CDS associations that are not exposed in the SELECT lists.

ABAP_RESTRICTION
Defining new CDS compositions is not possible in a CDS view with UNION or UNION ALL.
ABAP_RESTR_END

Latest notes:

Union sets can be a good way of transforming non-normalized DDIC database tables into a normalized view on the data.

If the length of the value range of an element from the SELECT list of the first SELECT statement does not cover the associated elements of the following SELECT statements, it is advisable to define an appropriate type with a suitable CAST expression.

The maximum number of different SELECT statements that can be merged using UNION depends on the database system. If this number is exceeded, the CDS view cannot be activated.
NON_V5_HINTS
ABAP_HINT_END

ABAP_EXAMPLES
Union set without name list. The element names of the SELECT lists must match. @AbapCatalog.sqlViewName: '...'
define view ... as
select
from demo_join1
{ a as c1, b as c2, c as c3, d as c4 }
union
select
from demo_join2
{ d as c1, e as c2, f as c3, g as c4 }
Union set with name list. The element names of the SELECT lists do not need to match. @AbapCatalog.sqlViewName: '...'
define view ... ( c1, c2, c3, c4 ) as
select
from demo_join1
{ a, b, c, d }
union
select
from demo_join2
{ d, e, f, g }
ABAP_EXAMPLE_END

ABAP_EXAMPLE_VX5
The following CDS view creates the union of the result sets of two SELECT statements. The element col1 in the first SELECT list has the type INT4, whereas the associated element col1 in the second SELECT list has the type INT8. This is why a syntax check warning is raised. To bypass the warning, col2 is converted to data type INT8 using a CAST expression.
DDLS DEMO_CDS_UNION_ELEMENT_TYPE
The class CL_DEMO_CDS_UNION_ELEMENT_TYPE uses SELECT to access the view four times:

The first access writes directly to an internal table with the line type of the CDS entity. The access works because the value of the element col1 matches the value range of the data type i.

The second access is the same as the first but one value in the element col1 is outside the value range of the data type i of the first column of the internal table result2. This is why an exception is raised.

In the third access, the exception is prevented since the data type of the first column of the result set (and hence the data type of the internal table result3) is transformed to int8 using a CAST in AB_SQL .

In the fourth access, the exception is prevented due to an appropriate declaration of the data type of the first column of the internal table result4.
The recommended method in all cases, however, is to handle the second element using a CAST in the CDS view.
ABAP_EXAMPLE_END