Hi, I am trying to map a composite key from a different CDT to another one

when creating CDT (Data Type), choose "create from database table or view". If your database has the composite primary key, CDT also has it. 

You can import it, but you can't actually use it. If you do this, you will see a message that says: "Data types without primary keys, or with more than one primary key, prevent data stores from publishing. In order to publish a data store that contains this data type, you must modify the data type so that it has only one primary key, then publish the data store. Otherwise, the data store will be saved as a draft."

The CDT it self will be created but when you attempt to publish the data store it will fail. This means you can't read or write to the database, so the CDT itself becomes essentially useless. Composite keys are not supported in Appian when reading / writing to a database.

You can import it, but you can't actually use it. If you do this, you will see a message that says: "Data types without primary keys, or with more than one primary key, prevent data stores from publishing. In order to publish a data store that contains this data type, you must modify the data type so that it has only one primary key, then publish the data store. Otherwise, the data store will be saved as a draft."

The CDT it self will be created but when you attempt to publish the data store it will fail. This means you can't read or write to the database, so the CDT itself becomes essentially useless. Composite keys are not supported in Appian when reading / writing to a database.