Cardinality &2 of Association &1 does not match to the ON-condition

What causes this issue?

The cardinality &V2& of the association &V1& does not match to the given
ON-Condition:
If not all key-elements of the targeted data source are compared with an
EQUAL Operator with a corresponding element in the current data source,
a cardinality of TO-1 is not expected.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

How to fix this error?

This warning can be suppressed by putting the pseudo comment
/*+[hideWarning] { "IDS" : [ "CARDINALITY_CHECK" ] }*/
in front of the view definition or the association definition.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.