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Day 3: Filtering Data Using the `WHERE` Clause and Logical Operators (`AND`, `OR`, `NOT`)

Welcome to Day 3 of your SQL journey! 🎉

Yesterday, we learned about SQL data types and basic queries using `SELECT`. Today, we will take it further and learn how to filter data using the WHERE clause and logical operators (AND, OR, NOT).

By the end of this lesson, you’ll be able to retrieve specific data based on conditions! 🚀

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📌 What is the `WHERE` Clause?

In real-world databases, tables contain thousands or even millions of records. If you only want to find specific data, you need a filtering method.

The WHERE clause allows us to retrieve only the records that match certain conditions instead of displaying the entire table.

📖 Syntax:

SELECT column1, column2, ... 
FROM table_name 
WHERE condition;

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📌 Using `WHERE` to Filter Data
Let’s take an example. We have a Students table with the following records:

| Student_ID | Name | Age | Grade | Enrollment_Date |
|------------|--------------|-----|-------|----------------|
| 1 | John Doe | 18 | A | 2023-09-01 |
| 2 | Emma Smith | 19 | B | 2022-08-15 |
| 3 | Alex Brown | 20 | A | 2021-07-10 |
| 4 | Sophia Johnson| 18 | C | 2023-01-20 |

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1️⃣ Filtering Data with `WHERE` Clause

Example 1: Find all students who are 18 years old

SELECT * FROM Students WHERE Age = 18;

🔹 Output:
| Student_ID | Name | Age | Grade | Enrollment_Date |
|------------|--------------|-----|-------|----------------|
| 1 | John Doe | 18 | A | 2023-09-01 |
| 4 | Sophia Johnson| 18 | C | 2023-01-20 |

✅ Explanation:
- The query only selects students where Age = 18.

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2️⃣ Using `AND` Operator

The `AND` operator allows us to filter based on multiple conditions.

Example 2: Find students who are 18 years old AND have Grade A

SELECT * FROM Students WHERE Age = 18 AND Grade = 'A';

🔹 Output:
| Student_ID | Name | Age | Grade | Enrollment_Date |
|------------|--------|-----|-------|----------------|
| 1 | John Doe | 18 | A | 2023-09-01 |

✅ Explanation:
- The query filters students who are both 18 years old AND have Grade A.

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3️⃣ Using `OR` Operator

The `OR` operator allows us to filter if at least one condition is met.

Example 3: Find students who are either 18 OR 19 years old

SELECT * FROM Students WHERE Age = 18 OR Age = 19;

🔹 Output:
| Student_ID | Name | Age | Grade | Enrollment_Date |
|------------|--------------|-----|-------|----------------|
| 1 | John Doe | 18 | A | 2023-09-01 |
| 2 | Emma Smith | 19 | B | 2022-08-15 |
| 4 | Sophia Johnson| 18 | C | 2023-01-20 |

✅ Explanation:
- The query selects students who are either 18 OR 19 years old.

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4️⃣ Using `NOT` Operator

The `NOT` operator helps us find records that do NOT match a certain condition.

Example 4: Find students who are NOT 18 years old

SELECT * FROM Students WHERE NOT Age = 18;

🔹 Output:
| Student_ID | Name | Age | Grade | Enrollment_Date |
|------------|-----------|-----|-------|----------------|
| 2 | Emma Smith | 19 | B | 2022-08-15 |
| 3 | Alex Brown | 20 | A | 2021-07-10 |

✅ Explanation:
- The query excludes students who are 18 years old.

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📌 Combining `AND`, `OR`, and `NOT`

Example 5: Find students who are either Grade A OR Grade B, but NOT 18 years old

SELECT * FROM Students WHERE (Grade = 'A' OR Grade = 'B') AND NOT Age = 18;

🔹 Output:
| Student_ID | Name | Age | Grade | Enrollment_Date |
|------------|-----------|-----|-------|----------------|
| 2 | Emma Smith | 19 | B | 2022-08-15 |
| 3 | Alex Brown | 20 | A | 2021-07-10 |

✅ Explanation:
- The query selects students who have Grade A OR B.
- But it excludes students who are 18 years old.

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📌 Using Comparison Operators with `WHERE`

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