Key is a unique value in the map. You can create your own with following constraints:
- Key Length: Minimum length of 1. Maximum length of 64.
- Key Pattern:
[0-9a-zA-Z-]*
For more information, please see https://docs.aws.amazon.com/quicksight/latest/APIReference/API_CreateDataSet.html#QS-CreateDataSet-request-PhysicalTableMap