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10_ABAP_SQL_Hierarchies.md
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# ABAP SQL: Working with Hierarchies
This cheat sheet summarizes the functions ABAP SQL offers together with
ABAP CDS for working with [hierarchical
data](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenhierarchy_glosry.htm "Glossary Entry")
that is stored in database tables. Hierarchical data in database tables
means that lines of one or more database tables are connected by
[parent-child
relationships](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenpcr_glosry.htm "Glossary Entry").
There are many use cases where hierarchical data plays a role and where
accessing information about the hierarchical relationship is important.
For example, a common task can be to find out the descendants or
ancestors of a given hierarchy node or to aggregate values of subtrees.
- [ABAP SQL: Working with Hierarchies](#abap-sql-working-with-hierarchies)
- [Introduction](#introduction)
- [Overview](#overview)
- [SQL Hierarchies](#sql-hierarchies)
- [Creating SQL Hierarchies](#creating-sql-hierarchies)
@@ -28,6 +17,19 @@ ancestors of a given hierarchy node or to aggregate values of subtrees.
- [Hierarchy Aggregate Navigators](#hierarchy-aggregate-navigators)
- [More Information](#more-information)
## Introduction
This cheat sheet summarizes the functions ABAP SQL offers together with
ABAP CDS for working with [hierarchical
data](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenhierarchy_glosry.htm "Glossary Entry")
that is stored in database tables. Hierarchical data in database tables
means that lines of one or more database tables are connected by
[parent-child
relationships](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenpcr_glosry.htm "Glossary Entry").
There are many use cases where hierarchical data plays a role and where
accessing information about the hierarchical relationship is important.
For example, a common task can be to find out the descendants or
ancestors of a given hierarchy node or to aggregate values of subtrees.
## Overview
@@ -57,6 +59,8 @@ learn some additional syntax and then you can start right away.
> **💡 Note**<br>
> The examples in this cheat sheet are only relevant for [standard ABAP](https://help.sap.com/doc/abapdocu_latest_index_htm/latest/en-US/index.htm?file=abenstandard_abap_glosry.htm), i. e. the unrestricted ABAP language scope. Find the artifacts used in the code snippets in your on-premise system.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
## SQL Hierarchies
With [SQL
@@ -99,6 +103,8 @@ for each row. For creating a SQL hierarchy, you need the following:
The following topics show you step-by-step how SQL hierarchies can be
created and accessed.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
## Creating SQL Hierarchies
### ABAP CDS Hierarchies
@@ -252,6 +258,8 @@ From the ABAP language point of view, CDS hierarchies are the most
convenient way of using SQL hierarchies. Now let us turn to other ways,
involving more ABAP, until we do not use any CDS more in the end.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
### ABAP SQL Hierarchy Generator HIERARCHY
The ABAP SQL [hierarchy
generator](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenhierarchy_generator_glosry.htm "Glossary Entry")
@@ -367,6 +375,8 @@ not least we will use CTEs as hierarchies themselves. You might skip the
following section and turn directly to the hierarchy navigators if you
are not too interested in this syntactic gimmicks.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
### ABAP CTE Hierarchies
A CTE that produces hierarchical data can declare itself as a SQL
@@ -479,6 +489,8 @@ hierarchy association. Running
`CL_DEMO_SQL_HIERARCHIES` shows that all
assertions are fulfilled.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
## Hierarchy Navigators
[Hierarchy
@@ -501,6 +513,8 @@ or a CTE hierarchy. Check the examples of the
[documentation](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenselect_hierarchy_navigators.htm),
where this is also shown.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
### Hierarchy Node Navigator HIERARCHY_DESCENDANTS
As the name says,
@@ -536,6 +550,8 @@ distance to the respective start node. A further parameter
`DISTANCE` - not shown here - allows you to restrict the
distance to the respective start node.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
### Hierarchy Node Navigator HIERARCHY_ANCESTORS
Now the other way around: ABAP SQL function
@@ -566,6 +582,8 @@ aggregate functions or evaluating the internal result table, you can now
easily extract further information like the number of ancestors and so
on.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
### Hierarchy Node Navigator HIERARCHY_SIBLINGS
Besides descendants and ancestors, hierarchy nodes also can have
@@ -598,6 +616,8 @@ the respective start node. Running
`CL_DEMO_SQL_HIERARCHIES`, where we start with
a node that definitely has some siblings, shows the result.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
### Hierarchy Aggregate Navigators
Finally let us turn to the [hierarchy aggregate
@@ -697,5 +717,7 @@ Running `CL_DEMO_SQL_HIERARCHIES` shows the
result. It also shows the result of the joined data source, where you
can check that the calculated values are correct.
<p align="right">(<a href="#top">⬆️ back to top</a>)</p>
## More Information
For the complete reference documentation about SQL hierarchies, see [`SELECT, FROM hierarchy_data`](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenselect_hierarchy_data.htm).