Polymorphic fields

[fehays]

Reference:
TYPEOF SOQL Reference

Polymorphic Relationships (TYPEOF)

String query = new Q(Event.SObjectType)
    .selectFields(Q.typeOf('What')
        .when('Account').then(new Set<String> {'Phone', 'NumberOfEmployees'})   
        .when('Opportunity').then(new Set<String> {'Amount', 'CloseDate'})                 
        .otherwise(new Set<String> {'Name', 'Email'})
    );
    
System.debug(query.build());
/*
SELECT
    TYPEOF What
    WHEN Account THEN Phone,NumberOfEmployees
    WHEN Opportunity THEN Amount,CloseDate
    ELSE Name,Email
    END
FROM Event
*/