// Indexes give you access to alternate query patterns, and can speed up queries.

Creating an Index

Indexes in DynamoDB are different from their relational counterparts. When you create a secondary index, you must specify its key attributes—a partition key and a sort key. After you create the secondary index, you can Query it or Scan it just as you would with a table.

Dynamo DB supports 2 kinds of Indices

  • Global secondary indexes – The primary key of the index can be any two attributes from its table.
  • Local secondary indexes – The partition key of the index must be the same as the partition key of its table. However, the sort key can be any other attribute.

Add a global secondary index to an existing table, using the UpdateTable action and specifying GlobalSecondaryIndexUpdatesFollowing. Following params are required

  • IndexName: A name for the index.
  • KeySchema: The attributes that are used for the index's primary key.
  • Projection: Attributes from the table that are copied to the index.
  • ProvisionedThroughput(for provisioned tables): number of reads and writes per second that you need for this index. 

    {
        TableName: "Music",
        AttributeDefinitions:[
            {AttributeName: "Genre", AttributeType: "S"},
            {AttributeName: "Price", AttributeType: "N"}
        ],
        GlobalSecondaryIndexUpdates: [{
            Create: {
                IndexName: "GenreAndPriceIndex",
                KeySchema: [
                    {AttributeName: "Genre", KeyType: "HASH"}, //Partition key
                    {AttributeName: "Price", KeyType: "RANGE"}, //Sort key
                ],
                Projection: { "ProjectionType": "ALL" },
                ProvisionedThroughput: { "ReadCapacityUnits": 1,"WriteCapacityUnits": 1 } // Only specified if using provisioned mode
            } } ]
    }
// DynamoDB does not have a query optimizer, so a secondary index is only used when you Query it or Scan it.
// You can request strongly consistent Query or Scan actions on a table or a local secondary index. However, global secondary indexes support only eventual consistency.

Querying an Index

perform Query operations directly on the index, in the same way as on a table. must specify both TableName and IndexName 


    {
        TableName: "Music",
        IndexName: "GenreAndPriceIndex",
        KeyConditionExpression: "Genre = :genre and Price < :price",
        ExpressionAttributeValues: {
            ":genre": "Country",
            ":price": 0.50
        }
    };