In the previous blog"SAP CDS View basic syntax (create your first CDS View)"
In , I introduced the basic syntax of CDS View. In this blog, I will introduce some advanced usage of CDS operations, including three parts: aggregation, JOIN and UNION.

1 gather

use:

Complete aggregation operations, such as MIN, MAX, COUNT, SUM, etc.

grammar:

@AbapCatalog.sqlViewName: 'ZDEMO_CDS_SQL'
@AbapCatalog.preserveKey: true
define view ZDEMO_CDS_DDL
  as select from sflight
{
  planetype,
  min(price) as min_price,
  max(price) as max_price,
  sum(price) as sum_price,
  count(*)   as count_planes

}
group by
  planetype

Explanation:

• When using aggregate operations, usegroup bySpecify the aggregated items, that is, according to which fields to group statistics.

running result:

2 Having statement in aggregate operation

use:

Specify the filter conditions during the aggregation operation

grammar:

@AbapCatalog.sqlViewName: 'ZDEMO_CDS_SQL'
@AbapCatalog.preserveKey: true
define view ZDEMO_CDS_DDL
  as select from sflight
{
  planetype,
  min(price) as min_price,
  max(price) as max_price,
  sum(price) as sum_price,
  count(*)   as count_planes

}
group by
  planetype
having
  planetype = '747-400'
  or count(*)  > 60

Explanation:

• HavingThe condition fields specified in can only be a subset of the fields in group by;HavingYou can also use the intermediate result set of the aggregation operation as the deletion condition

running result:

3 JOIN

use:
CDS supports Inner Join, Left Outer Join, Right Outer Join
grammar:

@AbapCatalog.sqlViewName: 'ZDEMO_CDS_SQL'
@AbapCatalog.preserveKey: true
define view ZDEMO_CDS_DDL
  as select from sbook   as a
    inner join   sflight as b on  a.carrid = b.carrid
                              and a.connid = b.connid
                              and a.fldate = b.fldate
{
  a.carrid    as airline_code,
  a.connid    as connection_number,
  a.fldate    as flight_date,
  a.customid  as customer_id,
  b.planetype as planetype
}
where
  a.carrid = 'DL'

Explanation:

• The usage of Inner Join, Left Outer Join, Right Outer Join is the same as that of ABAP OPEN SQL

running result:

4 UNION

use:
UNION the result set of two SELECT

grammar:

@AbapCatalog.sqlViewName: 'ZDEMO_CDS_SQL'
@AbapCatalog.preserveKey: true
define view ZDEMO_CDS_DDL
  as select distinct from sbook
{
  carrid as airline_code,
  connid as connection_number,
  fldate as flight_date
}
where
  carrid = 'DL'

union

select distinct from sflight
{
  carrid as airline_code,
  connid as connection_number,
  fldate as flight_date
}
where
  planetype = '747-400'

Explanation:

• UNIONYou can merge the result sets of two SELECTs and remove duplicate entries by yourself
• UNION ALL Combine the result set and keep duplicate entries
• The two merged result sets must have the same number of fields
• The column types of the combined result set must be compatible
• The field names must be the same

running result:

5 Summary

In this article, we further introduce the operation syntax of SAP CDS View. I believe that through these two blogs, all students should have learned to create CDS View and complete operation logic with CDS View. There are many other uses of CDS View, and interested students can check the help files of ABAP.

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