What is SQL?

SQL (Structured Query Language) is the standard language for managing and manipulating data in relational databases. Whether you're a data analyst, web developer, or business professional, SQL is an essential skill for working with data.

What Does SQL Stand For?

• Structured - Data is organized in tables with rows and columns
• Query - You ask questions (queries) to get data
• Language - A standardized way to communicate with databases

What Can SQL Do?

SQL is incredibly powerful and versatile. Here's what you can accomplish with SQL:

• 📊 Retrieve data from a database (SELECT queries)
• ➕ Insert new data into a database
• ✏️ Update existing data in a database
• 🗑️ Delete data from a database
• 🏗️ Create new databases and tables
• 🔧 Modify database structures (add/remove columns, change data types)
• 🔐 Set permissions on tables and databases
• 📈 Analyze data with aggregations and calculations

SQL is a Standard Language

Although SQL is an ANSI (American National Standards Institute) and ISO (International Organization for Standardization) standard, there are different versions and dialects of SQL used by different database systems:

Good news: The core SQL commands (SELECT, INSERT, UPDATE, DELETE) are the same across all these systems! Once you learn the fundamentals, you can work with any SQL database.

Understanding SQL Statements

SQL consists of statements - commands that tell the database what you want to do. Every SQL statement starts with a keyword (like SELECT, INSERT, UPDATE) and ends with a semicolon (;).

The Semicolon (;) - Statement Terminator

The semicolon is used to separate SQL statements. It tells the database "this statement is complete, execute it now." Think of it like a period at the end of a sentence.

-- Correct: Statement ends with semicolon
SELECT * FROM students;

-- Also correct: Multiple statements
SELECT * FROM students;
SELECT * FROM courses;

-- Incorrect: Missing semicolon
SELECT * FROM students

SQL Keywords and Commands

SQL uses special keywords to perform different operations. Here are the most important ones you'll learn:

1. Data Query Language (DQL)

SELECT - Retrieve data from database

2. Data Manipulation Language (DML)

INSERT - Add new data
UPDATE - Modify existing data
DELETE - Remove data

3. Data Definition Language (DDL)

CREATE - Create new database objects (tables, databases)
ALTER  - Modify existing database objects
DROP   - Delete database objects

4. Data Control Language (DCL)

GRANT  - Give user access permissions
REVOKE - Remove user access permissions

5. Transaction Control Language (TCL)

COMMIT   - Save changes permanently
ROLLBACK - Undo changes since last COMMIT
SAVEPOINT - Set a point to rollback to

TCL commands manage transactions in databases. A transaction is a set of SQL operations that are treated as a single unit. If something goes wrong, you can use ROLLBACK to undo all changes. When everything is correct, use COMMIT to save the changes permanently.

SQL is NOT Case Sensitive

SQL keywords are not case-sensitive. This means SELECT, select, and Select all work the same way. However, there are conventions that make code more readable:

-- All of these work the same:
SELECT * FROM students;
select * from students;
Select * From Students;

-- Best practice: Keywords in UPPERCASE
SELECT * FROM students;

Your First SQL Query

Let's write your first SQL statement! This simple query retrieves all data from a table called "students":

SELECT * FROM students;

Let's break down what each part means:

• SELECT - The command that tells the database we want to retrieve data
• * - The asterisk means "all columns" (we want every field)
• FROM - Specifies which table to get the data from
• students - The name of the table we're querying
• ; - Semicolon marks the end of the statement

Comments in SQL

Comments are notes in your code that the database ignores. They help you and others understand what your SQL does.

Single-Line Comments

-- This is a single-line comment
SELECT * FROM students; -- Get all students

Multi-Line Comments

/* This is a multi-line comment.
   It can span multiple lines.
   Useful for longer explanations. */
SELECT * FROM students;

Why Learn SQL?

Real-World SQL Use Cases

• 🏪 E-commerce: Track orders, inventory, and customer data
• 🏥 Healthcare: Manage patient records and medical histories
• 🎓 Education: Store student information, grades, and course enrollment
• 💰 Finance: Process transactions and generate financial reports
• 📱 Social Media: Store user profiles, posts, and connections
• 🎮 Gaming: Save player progress, scores, and achievements

Key Takeaways

What's Next?

Now that you understand what SQL is and how statements work, you're ready to start writing queries! In the next lesson, you'll learn about the SELECT statement - the most fundamental and frequently used SQL command.