Day 36 of #100DaysOfCode — SQL Basics

A relational database is a way to store data in an organized structure of tables with rows and columns, making it easy to manage, query, and maintain relationships between different datasets. To interact with these databases, we use SQL (Structured Query Language) — the standard language for creating, reading, updating, and deleting data.

Today, for Day 36, the goal was to understand table creation, CRUD operations, filtering, sorting, and common data types.

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What is SQL?

SQL stands for Structured Query Language. It is the standard language used to interact with relational databases.

Relational databases are systems where data is stored in tables with rows and columns. Popular relational databases include:

• MySQL
• PostgreSQL
• SQLite
• Microsoft SQL Server

Example Table:

id	name	age
1	Ali	23
2	Sara	25

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Database Structure Concepts

Understanding SQL requires knowing some key database terms:

Concept	Meaning
Database	Collection of tables
Table	Structured dataset
Row	Single record in a table
Column	Attribute of data
Primary Key	Unique identifier for a row
Foreign Key	Reference to another table

Example: Users Table

id	name	email

✅ Tip: Always define a primary key to ensure each row is unique.

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Creating Databases and Tables

Create a Database

CREATE DATABASE mydb;

Select (Use) the Database

USE mydb;

Create a Table

CREATE TABLE users (
  id INT PRIMARY KEY,
  name VARCHAR(50),
  age INT
);

Concepts to Learn:

• Data types (INT, VARCHAR, TEXT, etc.)
• Primary keys
• Table structure

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CRUD Operations in SQL

CRUD stands for Create, Read, Update, Delete — the four essential operations in SQL.

Create (Insert Data)

INSERT INTO users (id, name, age)
VALUES (1, 'Saad', 23);

Read (Select Data)

Select all columns:

SELECT * FROM users;

Select specific columns:

SELECT name, age FROM users;

Update Data

UPDATE users
SET age = 24
WHERE id = 1;

Delete Data

DELETE FROM users
WHERE id = 1;

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Filtering Data

Filtering helps you fetch only the data you need.

WHERE Clause

SELECT * FROM users
WHERE age > 20;

Multiple Conditions

SELECT * FROM users
WHERE age > 20 AND name = 'Ali';

💡 Tip: Use OR and AND to combine conditions.

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Sorting Results

SQL allows you to sort query results using ORDER BY.

SELECT * FROM users
ORDER BY age ASC;

Descending order:

SELECT * FROM users
ORDER BY age DESC;

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Limiting Results

To control the number of results returned, use LIMIT. This is especially useful for pagination:

SELECT * FROM users
LIMIT 5;

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SQL Data Types (Basic)

Common SQL data types you’ll encounter:

Type	Use
INT	Numbers
VARCHAR	Short text
TEXT	Long text
BOOLEAN	True/False
DATE	Date values

✅ Pro Tip: Choosing the correct data type is important for performance and storage efficiency.

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🏁 Conclusion

SQL is an essential skill for any developer, data analyst, or anyone working with databases. By mastering tables, CRUD operations, filtering, sorting, and data types, you can interact with relational databases efficiently.

Learning SQL and understanding relational databases is incredibly valuable because nearly every application, website, or service relies on data stored in structured tables. Whether you want to build applications, analyze data, or manage systems, SQL empowers you to efficiently retrieve, manipulate, and maintain data.

Thank you for reading! Feel free to share your thoughts!