SQL
Talk to any database
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read 10 chapters Database
Created
1986 by IBM (SEQUEL)
Type
Declarative query language
Standard
ISO/IEC 9075
Works with
PostgreSQL, MySQL, SQLite, SQL Server
Used for
Data analysis, app backends, reporting
Annual jobs
Most in-demand database skill
Difficulty
Easy to learn, deep to master
Best for
Structured data, relationships, analytics
What is SQL?
SQL (Structured Query Language) is the standard language for talking to relational databases. It's how you read, write, and analyse data stored in tables with rows and columns.
Every web application, mobile app, and data pipeline ultimately talks to a database, and almost every database speaks SQL.
Why SQL?
| Feature | SQL | NoSQL (MongoDB) | CSV/Excel |
|---|---|---|---|
| Data integrity | Strong constraints | Weak | None |
| Relationships | Excellent (JOINs) | Limited | Manual |
| Query power | Very high | Medium | Low |
| ACID transactions | Yes | Varies | No |
| Career demand | Highest for data | Growing | Niche |
What you'll learn
| Chapter | What you'll know |
|---|---|
| Basics | SELECT, WHERE, ORDER BY, LIMIT |
| Joins | Combining data across tables |
| Aggregation | GROUP BY, COUNT, AVG, SUM |
| Modifying | INSERT, UPDATE, DELETE |
| Design | Table design, normalisation, indexes |
Start with basics to learn how to query data.