# Databases - Intro
# What is a database?
- A database is a system for storing data in an ordered way.
- It consists of the data that is stored and a software that manages it.
- Databases have a query language to retrieve and manipulate the data.
# Classification
It is common practice to use these terms synonymously:
- Relational databases = SQL databases
- Document-based databases = NoSQL databases
| Relational Databases | Document-based Databases |
|---|---|
| The classic type of databases, made popular by MySQL. | The modern approach to databases, addresses problems in web development. |
| Useful for more complex data that has a lot of relationships between entities. | Useful for large amounts of data that is rather uniform. |
| Structured | Mostly unstructured |
| Complex to set up | Simple to query |
| Data integrity built in | Data integrity relies heavily on programming |
| Uses SQL | Uses a custom query language, often resembling JavaScript |
| Examples: MariaDB, MySQL, SQLite (mobile), SQL Server | **Examples: **MongoDB, CouchDB, Firebase Cloud Firestore |
# CRUD
Regardless of the type of database we use, we will always have four types of operations:
C - Create
R - Read
U - Update
D - Delete
**CRUD **is not only used in databases, but also for REST APIs.
# Methodology for Finding the Right Query
Finding the right query can be difficult, especially on the command line. To find the right query, you can follow the following steps:
1) Browse the dataset and familiarize yourself with it.
2) Identify the field you are interested in.
3) Identify the query operator or the syntax you need.
- Check the documentation
- Search the web for examples
4) Try it out.
(Trial and error)