## Introduction 
Welcome to Lesson 2.2: Understanding Databases (SQL vs NoSQL). This lesson is part of Module 2: Core Skills - Web Development Fundamentals in the Full Stack Development for Developers at Test_Company course. In this lesson, we'll explore the differences between SQL and NoSQL databases, basic SQL queries, and the use cases for each type of database. By the end of this lesson, you will be able to differentiate between SQL and NoSQL databases and write basic SQL queries.
## Main Content
### Differences between SQL and NoSQL Databases
SQL (Structured Query Language) databases are relational databases that use a structured schema and predefined relationships between tables. These databases, such as MySQL and PostgreSQL, rely on SQL for defining and manipulating the data, making them very powerful for complex queries and transactions. SQL databases are ideal for situations where data integrity, consistency, and complex queries are essential, such as in banking systems where transactions must be accurate and reliable.
On the other hand, NoSQL (Not Only SQL) databases are non-relational and can handle unstructured or semi-structured data. Examples include MongoDB and Cassandra. These databases are designed for scalability and flexibility, allowing for varied data types and structures. NoSQL databases are particularly useful for big data applications, content management systems, and real-time web apps where rapid data retrieval and scalability are critical.
To summarize, the key differences are:
- **Structure**: SQL databases use a fixed schema; NoSQL databases are schema-less.
- **Data Relationships**: SQL databases rely on relationships; NoSQL databases can handle data without relationships.
- **Scalability**: SQL databases scale vertically (adding resources to a single server), while NoSQL databases scale horizontally (adding more servers).
### Basic SQL Queries
SQL allows you to interact with the database using a set of commands. Here are a few basic SQL commands that you will find useful:
1. **SELECT**: This command retrieves data from the database.
 ```sql
 SELECT * FROM customers WHERE city = 'New York';
 ```
 This query fetches all records from the 'customers' table where the city is New York.
2. **INSERT**: This command adds new records to a table.
 ```sql
 INSERT INTO customers (name, city) VALUES ('John Doe', 'Los Angeles');
 ```
 This query inserts a new customer named John Doe living in Los Angeles.
3. **UPDATE**: This command modifies existing records in a table.
 ```sql
 UPDATE customers SET city = 'San Francisco' WHERE name = 'John Doe';
 ```
 This query updates the city for John Doe to San Francisco.
4. **DELETE**: This command removes records from a table.
 ```sql
 DELETE FROM customers WHERE city = 'Los Angeles';
 ```
 This query deletes all records of customers living in Los Angeles.
These commands form the foundation of interacting with SQL databases and can be used to manage and manipulate data effectively.
### Use Cases for Each Type of Database
Different projects require different database technologies. Here are some common use cases for SQL and NoSQL databases:
**SQL Use Cases**:
- **Financial Transactions**: SQL databases excel in applications that require complex transactions, such as banking systems. The ACID properties (Atomicity, Consistency, Isolation, Durability) of SQL ensure that transactions are processed reliably.
- **Enterprise Applications**: Many enterprise solutions require structured data and complex queries, making SQL databases a suitable choice.
**NoSQL Use Cases**:
- **Big Data Applications**: NoSQL databases are designed to handle large volumes of unstructured data. They can manage diverse data types, making them ideal for analytics and big data projects.
- **Content Management Systems**: When developing a CMS where content types can vary widely (articles, videos, etc.), a NoSQL database can provide the flexibility needed to store different formats and structures.
Understanding the right context for each database type will help you make informed decisions in your projects.
## Conclusion 
In this lesson, we covered the fundamental differences between SQL and NoSQL databases, explored basic SQL queries, and discussed practical use cases for each database type. Understanding these concepts is crucial for utilizing databases effectively in your development projects. By the end of this lesson, you should now be able to differentiate between SQL and NoSQL databases and write basic SQL queries.
## Reflection Questions
1. How would you determine which type of database to use for a particular application in a finance context?
2. Can you think of a scenario in your work where a specific SQL query could help retrieve important data?
3. Reflect on the advantages and disadvantages of using NoSQL databases versus SQL databases in your projects.