Indexes Deepdive

What is an Index?

In SQL databases, an index is a data structure which allows you to perform fast queries on specific columns in a table. You select the columns that you want included in the index and run your searches on the index - rather than on the entire dataset.

In DynamoDB, 2 types of Index are supported to help speed-up your DynamoDB quries: * Local Secondary Index * Global Secondary Index

Local Secondary Index

• Can only be created when you are creating your table
• You cannot add, remove, or modify it later
• It has the same Partition Key as your original table
• But a different Sort Key
• Gives you a different view of your data, organised according to an alternative Sort Key
• Any queries based on this Sort Key are much faster using the index than the main table
• e.g. Partition Key: User ID; Sort Key: account creation date

Global Secondary Index

• You can create when you create your table, or add it later
• Different Partition Key as well as Different Sort Key
• Gives a completely different view of the data
• Speeds up any queries relating to this alternative Partition and Sort Key
• e.g. Partition Key: email adress; Sort Key: last login date

Exam Tips

• Indexes enable fast queries on specific data columns
• Give you a different view of yourd ata, based on alternative Partition / Sort Keys
• Important to understand the differences

Local Secondary	Global Secondary
Must be created when you create your table	can create at any time - at table creation or after
Same Partition key as your table	Different Partition Key
Different Sort Key	Different Sort Key