Secondary Indexes

A DynamoDB table's primary key supports one access pattern. When you need to query data by different attributes, you create secondary indexes. DynamoDB supports two types: Global Secondary Indexes (GSI) and Local Secondary Indexes (LSI).

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Why Secondary Indexes?

Consider a table with a primary key of UserId:

Table: Users (PK = UserId)

UserId     Name      Email                 Country
user-001   Alice     alice@example.com     UK
user-002   Bob       bob@example.com       US
user-003   Charlie   charlie@example.com   UK

You can efficiently look up a user by UserId, but what if you need to:

• Find all users in a specific country?
• Look up a user by email?
• List users sorted by name?

Without indexes, you would need a Scan (reading every item). Secondary indexes let you Query efficiently by different attributes.

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Global Secondary Index (GSI)

A GSI has its own partition key and sort key, which can be any attributes from the table: