SQL Notes for Beginners: A Complete Guide to Getting Started

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Structured Query Language (SQL) is the standard language for managing and manipulating relational databases. Whether you’re a data analyst, software developer, or aspiring data engineer, understanding SQL is crucial for interacting with data efficiently. This article will serve as a comprehensive set of SQL notes that you can refer to for learning or revision.

Contents

📌 What is SQL?🔹 Basic SQL Syntax 🏗️ SQL Data Types 🛠️ Creating Tables ✏️ Inserting Data 📤 Retrieving Data 🔄 Updating and Deleting Data 🔍 SQL Clauses and Keywords 🔗 SQL Joins 📊 Aggregate Functions 🧩 Subqueries and Aliases 🧼 Best Practices 🚀 Conclusion

Pdf Notes :- https://drive.google.com/file/d/1UV6_BEKLAiWXxRhDnjpggaqbhdmoWESX/view?usp=sharing

📌 What is SQL?

SQL stands for Structured Query Language. It is used to communicate with relational databases. SQL lets you create, read, update, and delete data — commonly known as CRUD operations.

Some of the most popular database systems that use SQL are:

MySQL
PostgreSQL
SQLite
Oracle
Microsoft SQL Server

🔹 Basic SQL Syntax

Here’s an example SQL query to fetch data from a table:

This statement reads:

SELECT the columns first_name and last_name
FROM the table called employees
WHERE the department is ‘Sales’

🏗️ SQL Data Types

When creating tables, it’s important to define the correct data types for each column:

INT: Integer values
VARCHAR(n): Variable-length string up to n characters
DATE: Date values (YYYY-MM-DD)
FLOAT or DECIMAL: Decimal numbers
BOOLEAN: True/False values

🛠️ Creating Tables

To store data in a database, you first need to create tables.

✏️ Inserting Data

Once a table is created, you can insert records using INSERT INTO:

📤 Retrieving Data

Use the SELECT statement to query data:

This selects all columns for all rows in the students table. You can filter results using the WHERE clause:

🔄 Updating and Deleting Data

You can modify data using UPDATE:

To remove data, use DELETE:

🔍 SQL Clauses and Keywords

Some commonly used SQL clauses include:

ORDER BY: Sorts results (ascending by default)
GROUP BY: Groups rows that have the same values
HAVING: Filters groups (used with GROUP BY)
JOIN: Combines rows from two or more tables
LIMIT: Restricts number of rows returned

Example of ORDER BY:

🔗 SQL Joins

Joins are used to fetch data from multiple related tables.

INNER JOIN: Returns records with matching values in both tables
LEFT JOIN: Returns all records from the left table and matched records from the right
RIGHT JOIN: Opposite of LEFT JOIN
FULL OUTER JOIN: Returns all records when there is a match in either table

Example:

📊 Aggregate Functions

SQL supports built-in functions for calculations:

COUNT(): Number of rows
SUM(): Total value
AVG(): Average
MIN() / MAX(): Smallest/largest value

Example:

🧩 Subqueries and Aliases

A subquery is a query nested inside another:

Aliases make column/table names more readable:

🧼 Best Practices

Always back up data before performing DELETE or UPDATE
Use WHERE to limit scope of changes
Name tables and columns clearly
Indent and format your queries for readability

🚀 Conclusion

SQL is a powerful and essential tool for anyone working with data. Whether you’re writing simple queries or complex joins, understanding SQL helps you unlock the full potential of relational databases. Practice is key, so try out queries on sample datasets or use online platforms like or Mode SQL Tutorial to improve your skills.

Keep this SQL notes guide handy as your quick reference, and happy querying!

SQL Notes for Beginners: A Complete Guide to Getting Started