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| id | title | tags | created | |
|---|---|---|---|---|
| xowl | DynamoDB |
|
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
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
personIdalone. -
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
personIdalong withLastName
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