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Shalini Tewari Profile picture
@maybeshalinii
Sep 16 • 6 tweets • 2 min read • Read on X
If starting with SQL, don't miss these essential topics:
1. SQL Basics
- SELECT Statement: It's like asking the database for specific information.
- FROM Clause: Tells the database where to look for that information.
- WHERE Clause: Filters out the stuff you don't need.
- ORDER BY Clause: Arranges the results in a specific order.

2. Data Manipulation
- INSERT: Adds new data.UPDATE: Changes existing data.
- DELETE: Removes data.
- MERGE: Combines these actions.

3. Data Definition
- CREATE TABLE: Makes a new table.
- ALTER TABLE: Edits an existing table.
- DROP TABLE: Deletes a table.
- INDEXES: Helps with finding data quickly.
4. Constraints
- PRIMARY KEY: Ensures each row is unique.
- FOREIGN KEY: Keeps data relationships intact.
- UNIQUE: Ensures values are unique.
- DEFAULT: Sets a value if none is given.

5. Joins (Really Important)
- INNER JOIN: Combines data from different tables.
- LEFT JOIN: Gets all data from one table and matching data from another.
- RIGHT JOIN: Opposite of LEFT JOIN.
- FULL JOIN: Gets data if it's in either table.
- SELF JOIN: Links data within the same table.

6. Subqueries:
- Correlated Subqueries: Subqueries connected to the main query.
- Scalar Subqueries: Subqueries that return a single value.
- Subquery in FROM Clause: Using a subquery as a table.
7. Aggregation Functions:
- SUM, COUNT, AVG, MAX, MIN: Math on groups of data.
- GROUP BY: Groups data before doing math.
- HAVING: Filters groups based on math results.

8. Views:
- CREATE VIEW: Makes a pretend table.
- ALTER VIEW: Changes the pretend table.
- DROP VIEW: Deletes the pretend table.

9. Transactions:
- BEGIN TRANSACTION, COMMIT, ROLLBACK: Ensures data stays safe and consistent.
- ACID Properties (Important): Rules for safe transactions.
10. Database Security:
- GRANT and REVOKE: Decides who can do what.
- Roles: Groups of permissions for users.

11. Normalization (Important):
- 1NF, 2NF, 3NF, BCNF, 4NF:
Ways to organize data for efficiency and accuracy.

12. Indexes:
- Clustered vs. Non-Clustered Indexes: Different ways to find data quickly.

13. Database Management Systems (DBMS):
- Different software tools for working with databases, like MySQL etc.
If you're interested in working with data, I have an ongoing series called SNOWFLAKE 101 where I also cover SQL, so make sure to check it out! It will be much appreciated!

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More from @maybeshalinii

Shalini Tewari Profile picture
Feb 16
Ever wondered how websites stay fast even with millions of users?

Let’s talk about caching and CDNs:
why website speed is critical?
- more than 50% of users leave if a website takes more than 3 seconds to load.
- a 1-second delay in page load time can reduce conversions by 7%.
- Search engines like Google prioritize fast websites in rankings.
But how do websites manage to stay fast, even when millions of people visit them at the same time?

The answer lies in two powerful technologies: Caching and CDNs (Content Delivery Networks).
These ensure websites load quickly, handle high traffic, and deliver a seamless experience.
Caching is like taking a shortcut. Instead of reloading everything from scratch every time you visit a website, caching saves a copy of the website’s data for quick access later.

Here’s how it works:
- When you visit a website, your browser downloads files like images, CSS, and JavaScript.
- Instead of downloading these files again on your next visit, your browser saves them locally in its cache.
- This reduces the time it takes to load the page and saves bandwidth.

Types of Caching:
- Browser Caching:
Your browser stores parts of the website (e.g., images, CSS) on your device.
Example: The website logo doesn’t need to load again: it’s already saved.

- Server Caching:
The website’s server stores frequently requested data, so it doesn’t have to regenerate it every time.
Example: A news website caches the homepage for faster delivery to users.

- CDN Caching:
Content is stored on servers around the world, closer to users.

Why is caching important?
- It makes websites faster.
- Reduces the load on servers.
- Saves bandwidth for users and website owners.
But caching alone isn’t enough for global websites with millions of users. That’s where CDNs come in.
Read 5 tweets
Shalini Tewari Profile picture
Jan 19
People often get confused between SQL and MySQL.

Here's the difference:
SQL

- Language:
SQL (Structured Query Language) is a standardized querying language used for managing and manipulating relational databases.

- Purpose:
It is used to perform tasks such as querying data, updating records, and managing database structures.

- Standardized:
SQL is a standard language that can be used with various database management systems (DBMS) like Oracle, Microsoft SQL Server, PostgreSQL, and MySQL.

- Commands:
Includes commands such as SELECT, INSERT, UPDATE, DELETE, CREATE, and DROP for database operations.

- Platform-Agnostic:
It is not tied to any specific DBMS, making it versatile for use across different systems.
MySQL

- DBMS:
MySQL is a specific relational database management system (RDBMS) that uses SQL as its query language.

- Open Source:
Developed by Oracle Corporation, MySQL is open-source, meaning it is freely available for use and modification.

- Use Case:
Commonly used in web applications and is part of the LAMP (Linux, Apache, MySQL, PHP) stack.

- Features:
Offers features such as multi-user access, replication, clustering, and a variety of storage engines.

- Implementation:
Implements the SQL language to perform database tasks but also includes additional tools and features for database management.
Read 4 tweets
Shalini Tewari Profile picture
Jan 8
Ever wondered how websites stay fast even with millions of users?

Let’s talk about caching and CDNs:
why website speed is critical?
- more than 50% of users leave if a website takes more than 3 seconds to load.
- a 1-second delay in page load time can reduce conversions by 7%.
- Search engines like Google prioritize fast websites in rankings.
But how do websites manage to stay fast, even when millions of people visit them at the same time?

The answer lies in two powerful technologies: Caching and CDNs (Content Delivery Networks).
These ensure websites load quickly, handle high traffic, and deliver a seamless experience.
Caching is like taking a shortcut. Instead of reloading everything from scratch every time you visit a website, caching saves a copy of the website’s data for quick access later.

Here’s how it works:
- When you visit a website, your browser downloads files like images, CSS, and JavaScript.
- Instead of downloading these files again on your next visit, your browser saves them locally in its cache.
- This reduces the time it takes to load the page and saves bandwidth.

Types of Caching:
- Browser Caching:
Your browser stores parts of the website (e.g., images, CSS) on your device.
Example: The website logo doesn’t need to load again: it’s already saved.

- Server Caching:
The website’s server stores frequently requested data, so it doesn’t have to regenerate it every time.
Example: A news website caches the homepage for faster delivery to users.

- CDN Caching:
Content is stored on servers around the world, closer to users.

Why is caching important?
- It makes websites faster.
- Reduces the load on servers.
- Saves bandwidth for users and website owners.
But caching alone isn’t enough for global websites with millions of users. That’s where CDNs come in.
Read 5 tweets
Shalini Tewari Profile picture
Jan 7
Did you know why restarting your computer actually fixes most problems?

Let's see why:
- It Stops Problematic Background Processes
Many programs and system services run in the background. Sometimes, they get stuck, crash, or just don’t work as intended.

These rogue processes can slow down your computer or cause errors.

Restarting forces all processes to stop and reload, fixing many of these issues.

- It Fixes System Resource Issues
Your computer has limited resources (CPU, RAM, storage). If too many programs are open or a program gets stuck, it can hog these resources.

Restarting frees up everything being used unnecessarily, letting your computer allocate resources properly again.
- It Clears Temporary Data (RAM)
Your computer uses RAM to temporarily store data for programs you’re running.

Over time, programs leave behind unused data in RAM (called memory leaks) even after they’re closed.
Restarting clears out all that junk, giving your computer a clean slate. That’s why your system often feels faster after a reboot.

- It Resolves Software Conflicts
When multiple programs or drivers try to access the same resource (like your printer or graphics card), conflicts can occur.
Over time, these conflicts build up and cause glitches, crashes, or slowdowns.
Restarting resets these temporary settings, resolving conflicts and letting everything start fresh.

- Resets Hardware Connections
Sometimes, hardware devices like your keyboard, mouse, or printer stop working because of temporary glitches in their drivers.
Restarting reloads all device drivers and re-establishes connections, fixing issues without needing deeper troubleshooting.
Read 4 tweets
Shalini Tewari Profile picture
Jan 5
Did you know your browser doesn’t render HTML, CSS, and JavaScript in the order they appear?

Here’s what actually happens:
How the Browser Handles HTML and CSS
- When you load a webpage, the browser doesn’t just display the HTML, CSS, and JavaScript in the order they appear. Instead, it follows a systematic process to ensure everything is rendered correctly.

- First, the browser starts with HTML parsing. It reads the HTML file line by line, building a structure called the DOM (Document Object Model). Think of the DOM as a tree where each HTML element becomes a node. For example,
,

, and are all nodes in this tree. This process continues until the entire HTML is read.

- As the browser encounters links to external CSS files, it temporarily pauses HTML parsing to fetch and process the CSS. Once the CSS is loaded, the browser creates another structure called the CSSOM (CSS Object Model). This structure contains all the styling rules and how they apply to the elements in the DOM.

- The combination of the DOM and CSSOM forms the Render Tree, which tells the browser how elements should look on the screen. Without this process, you’d only see plain, unstyled HTML.

The Role of JavaScript and How It Affects Rendering
- When the browser encounters a