Adding content to 111-databases

src/roadmaps/system-design/content/111-databases/102-sql-vs-nosql.md

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-# Sql vs nosql
+# SQL vs noSQL
+
+## Reasons for SQL:
+- Structured data
+- Strict schema
+- Relational data
+- Need for complex joins
+- Transactions
+- Clear patterns for scaling
+- More established: developers, community, code, tools, etc
+- Lookups by index are very fast
+
+
+## Reasons for NoSQL:
+- Semi-structured data
+- Dynamic or flexible schema
+- Non-relational data
+- No need for complex joins
+- Store many TB (or PB) of data
+- Very data intensive workload
+- Very high throughput for IOPS
+
+## Sample data well-suited for NoSQL:
+- Rapid ingest of clickstream and log data
+- Leaderboard or scoring data
+- Temporary data, such as a shopping cart
+- Frequently accessed ('hot') tables
+- Metadata/lookup tables
+
+Learn more from the followinw links:
+- [SQL vs NoSQL: The Differences](https://www.sitepoint.com/sql-vs-nosql-differences/)
+- [Scaling up to your first 10 million users](https://www.youtube.com/watch?v=kKjm4ehYiMs)

src/roadmaps/system-design/content/111-databases/index.md

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 # Databases
+
+A database is a collection of data that is organized and stored in a structured way, allowing for efficient retrieval and manipulation of the data. Databases are used in many different types of systems to store and manage data, from small personal applications to large enterprise systems.
+
+There are many different types of databases available, each with their own strengths and weaknesses. Some of the most common types of databases are:
+
+- Relational databases
+- NoSQL databases
+- Graph databases
+- Time-series databases
+
+Learn more from the following links:
+
+- [Intro to Databases](https://github.com/donnemartin/system-design-primer#database)
+- [Database design](https://en.wikipedia.org/wiki/Database_design)