The tables without primary keys can contain fields with unique indices. All connectors should handle such cases in the same way
- if DDL is available for the table then the primary key will be the first uniqe constraint defined either on column or as external contraint
- if only JDBC metadata are available then getIndexInfo should be used to obtain information about indices - to identify if there is any unique
If no index is available then the key of the message will be null.