SAP CDS view里计算两个date & time字段间包含的seconds秒数

@AbapCatalog.sqlViewName: 'DEMO_CDS_DATTYM'
@AbapCatalog.compiler.compareFilter: true
@AccessControl.authorizationCheck: #NOT_REQUIRED
@EndUserText.label: 'DEMO'
@VDM.viewType: #BASIC
@Analytics.dataCategory: #FACT
@Analytics.dataExtraction.enabled: true
Define view demo_cds_date_time
  as select from demo
{
ZDATE,
ZTIME,
ZDATE1,
ZTIME1,
tstmp_seconds_between
(
dats_tims_to_tstmp
(
ZDATE, 
ZTIME,
abap_system_timezone( $session.client,'NULL' ),
$session.client,
'NULL'
),

dats_tims_to_tstmp
(
ZDATE1, 
ZTIME2,
abap_system_timezone( $session.client,'NULL' ),
$session.client,
'NULL'
),

'NULL'
)as ZDIFF_SECONDS
}