A primary key uniquely identifies each item in the table, so no
two items can have the same key. DynamoDB supports two
different kinds of primary keys:
▪ Partition key
▪ Partition key and sort key
▪ Partition key
A simple primary key, composed of one attribute known as the
partition key.
▪ Partition key and Sort Key
It is Referred to as a composite primary key, this type of key is
composed of two attributes. The first attribute is the partition
key, and the second attribute is the sort key.
▪ DynamoDB uses the partition key value as input to an internal
hash function. A composite primary key gives you additional
flexibility when querying data
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.CoreComponents.html