🫰 databases

what is a database

• a usually large collection of data organized especially for rapid search and retrieval
• Databases are organized data storage (often, but not exclusively for computers)

the use of databases

• store information in an organized way to make data useful
• How a database is organized is dependent on how the information it stores will be used

forms of the databases

What makes it hard to talk about databases is how many different forms they can take

they can be in any form

e.g:

• digital database that is consumed by an application
• library
• physical ledger book
• a text file
• a spreadsheet of addresses
• the to-do sticky notes on my fridge
• ...etc

most popular types of databases

SQL/ relational databases

SQL type databases are organized to be query-able using SQL (Structured Query Language) and organize information in tables.

ideal usecases

Repeating, structured data, such as:

• user information
• product inventories
• blogs

Common SQL/Relational Database Technologies:

• MySQL
• PostgreSQL
• MariaDB
• Microsoft SQL Server

NoSQL/ non-relational databases

These databases can take a few different forms and are used for large sets of distributed data (like for use in micro service architectures).

Ideal Use Cases:

Partially structured or un-structured data: really big collections of complex data, caches

Types of NoSQL Databases:

• Key-Value store A key-value store is a non-relational, noSQL database type that stores data in key-value pairs (exactly like objects or dictionaries in programming). These databases are fast because the keys are unique and easily searchable, and they are flexible, because these key value pairs can store any combination of data types required.
• Document store A document store is a non-relational, noSQL database type that organizes data into documents. Documents can hold any shape of data, which means document stores can easily handle data with no structure or that is arbitrarily nested, which can be a headache to account for in a relational way.
• Column-oriented Data organized by column instead of by row. This architecture scales easily and makes fast, efficient queries. I'm including this architecture as a NoSQL type dbms, but this architecture can actually be used with SQL as well.

Common NoSQL Database Technologies:

• Redis [Key Value store]
• MongoDB [Document store]
• Elasticsearch [Document store]
• Apache Cassandra [Column-oriented]

schema

• the tables of a database, the columns and the column types of all of those tables can collectively be referred to as the schema
• describes the structure of a database
• the schema of a database is the tables of a database and their columns and column types
• the architecture or structure of a relational database, a statement of its tables and their columns
• Database Schema - The high level structure of a database, you can think of it as the general blueprint of a database with information about what tables it holds and what columns exist on those tables

Where Databases Run

• You can run a database on your computer and connect to it locally kind of like localhost.
• You can run a database on your own computer in a container system like Docker.
• Container systems are also common remotely, for instance in the Udacity workspace, you are connecting to a database running in a virtual machine.
• Services like AWS and Azure provide databases in the cloud.

what are migrations

• Migrations are a record of a change made to the schema of a database, with documented instructions to implement and rollback that change
• Migrations are documents outlining the changes made on a database overtime
• Migrations are only for tracking changes to the database schema nevert to individual rows in a table
• Migrations are records of changes made to the database schema
• Migrations contain instructions for hot to enact and rollback a specific change to the database
• Using migrations to manage database schema changes in a project makes it easier to keep databases across various environments synced together

Models

• Tables hold a list of items that share properties (columns), models are a class in our code that can be used as a template to create items that are stored as rows in the table.
• each instance of the model will be a row in the database
• The model is represented as a class, each book row in the database will be an instance of the book model.

resources

notes

• Structure of a relational database table is like a spreadsheet with columns
• database tables are always plural and model names are singular