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✍️ SELECT WHERE

This is the most important beginner topic 👇

🧠 1. SELECT Statement

• SELECT is used to retrieve data from a table

👉 Basic Syntax
SELECT column_name FROM table_name;

👉 Example
SELECT name FROM employees;

• ✔ Returns only the name column

👉 Select Multiple Columns
SELECT name, salary FROM employees;

👉 Select All Columns
SELECT * FROM employees;

🎯 2. WHERE Clause (Filtering Data)

• WHERE is used to filter records based on conditions

👉 Syntax
SELECT * FROM table_name
WHERE condition;

👉 Example
SELECT * FROM employees
WHERE salary > 50000;

✔ Returns employees earning more than 50k

⚡ 3. Operators You Must Know

🔹 Comparison Operators
• = (equal)
• > (greater than)
• < (less than)
• >= , <=
• != or <> (not equal)

🔹 Logical Operators
• AND → both conditions true
• OR → any condition true
• NOT → reverse condition

👉 Example
SELECT * FROM employees
WHERE department = 'IT' AND salary > 50000;

💡 4. Real-Life Thinking

Instead of memorizing, think like this:

• 👉 “What data do I need?”
• 👉 “From which table?”
• 👉 “What condition?”

Example:
“Show all HR employees earning less than 40k”

SELECT * FROM employees
WHERE department = 'HR' AND salary < 40000;

🎯 5. Practice Tasks
1. Show all employees with salary > 30k
2. Show employees from IT department
3. Show employees with salary between 40k–80k
4. Display only names of HR employees
5. Combine conditions using AND / OR

🔥 Practice Tasks Solution

✅ 1. Show all employees with salary > 30k
SELECT * FROM employees
WHERE salary > 30000;

✅ 2. Show employees from IT department
SELECT * FROM employees
WHERE department = 'IT';

✅ 3. Show employees with salary between 40k–80k
SELECT * FROM employees
WHERE salary BETWEEN 40000 AND 80000;

• 👉 Alternative:
SELECT * FROM employees
WHERE salary >= 40000 AND salary <= 80000;

✅ 4. Display only names of HR employees
SELECT name FROM employees
WHERE department = 'HR';

✅ 5. Combine conditions using AND / OR
SELECT * FROM employees
WHERE department = 'IT' AND salary > 50000;

• 👉 OR example:
SELECT * FROM employees
WHERE department = 'HR' OR salary < 30000;

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