Primary Key
Each item in DynamoDB is uniquely identified by its primary key.
In case of a Simple Primary Key, item is identified by it’s partition key.
In case of Composite Primary Key item is identified by its Partition Key and Sort Key.
You MUST provide the key-attribute names and types for the primary key attributes at the time of table creation. This primary key specification is referred to as the key-schema.
Once the table is created, you CANNOT change the primary key attributes for it.