text: The primary key can be a partition key, nothing more. Or, it can be a composite key which is a 
  
  combination of a partition key and sort key. When querying, you must give the partition key, and 
  
  optionally provide the sort key. 
  
  Amazon DynamoDB provides fast access to items in a table by specifying primary key values. 
  
  However, many applications might beneﬁt from having one or more secondary (or alternate) keys 
  
  available, to allow eﬃcient access to data with attributes other than the primary key. To address 
  
  this, you can create one or more secondary indexes on a table and issue Query or Scan requests 
  against these indexes. 
  
  A*secondary index*is a data structure that contains a subset of attributes from a table, along with 
  
  an alternate key to support Query operations. You can retrieve data from the index using a Query, 
  in much the same way as you use Query with a table. A table can have multiple secondary indexes, 
  which give your applications access to many diﬀerent query patterns. 
  
  DynamoDB supports two types of secondary indexes: 
  
  •**Global secondary index —**An index with a partition key and a sort key that can be diﬀerent 
  
  from those on the base table. A global secondary index is considered "global" because queries 
  
  on the index can span all of the data in the base table, across all partitions. A global secondary 
  
  index is stored in its own partition space away from the base table and scales separately from the 
  
  base table. 