eolas/zk/DynamoDB.md

---
id: xowl
title: DynamoDB
tags: [AWS]
created: Sunday, June 09, 2024
---

# DynamoDB

## Data structure

### Non-relational tables

DynamoDB is "NoSQL" because it does not support #SQL queries and is
non-relational meaning there cannot be JOIN operations via
[foreign_keys](Foreign_keys_in_SQL.md)

![](../img/dynamodb.png)

### Primary key

Although the data is stored as a table, one of the attributes is a primary key
and the rest of the attributes are effectively the values associated with it.

Because DynamoDB is schemaless, neither the attributes or their data types need
to be defined beforehand and each item can have its own distinct attributes.

Each item in the table is uniquely identifiable by its primary key.

There are two types of primary key available:

- partition key: a simple primary key composed of one attribute only. Because
  the primary key is hash-mapped items can be retrieved very rapidly using the
  primary key. This would be the `personId` alone.

- composite key: this comprises a partition key and a _sort key_ both of which
  are attributes. In a table that has a partition key and a sort key, it's
  possible for multiple items to have the same partition key value. However,
  those items must have different sort key values. You could then query by
  either key or both. For instance using the `personId` along with `LastName`

### Secondary index

As well as the index provided by the primary key, you can set one or more
**secondary indices**. A secondary index lets you query the data in the table
using an alternate key. The main type of secondary index is a _global secondary
index_. GSIs are useful for querying data that needs to be accessed using
non-primary key attributes. For example, if you have a Users table with UserID
as the primary key but often need to fetch users by their Email, a GSI on Email
would be appropriate.

**Global secondary indices** span the entire table allowing you to query accross
all partition keys whereas local secondary indices have the same partition key
as the

## Usage

## Related notes