Practical and Project-Based SQL

From Zero to Hero: Building a Simple Customer Database with SQL

Let’s start by creating a simple Customers table.

CREATE TABLE Customers (
    ID INT PRIMARY KEY,
    Name VARCHAR(50),
    City VARCHAR(50),
    Phone VARCHAR(20)
);

Insert sample data:

INSERT INTO Customers (ID, Name, City, Phone)
VALUES
(1, 'Alice', 'London', '555-1234'),
(2, 'Bob', 'Paris', '555-5678'),
(3, 'Charlie', 'New York', '555-8765');

Table looks like:

+----+---------+----------+----------+
| ID | Name    | City     | Phone    |
+----+---------+----------+----------+
| 1  | Alice   | London   | 555-1234 |
| 2  | Bob     | Paris    | 555-5678 |
| 3  | Charlie | New York | 555-8765 |
+----+---------+----------+----------+

Top 10 Essential SQL Commands Every Beginner Should Know

1. CREATE TABLE – build a table

2. INSERT INTO – add data

3. SELECT – view data

4. WHERE – filter results

5. ORDER BY – sort results

6. UPDATE – change data

7. DELETE – remove data

8. JOIN – combine tables

9. GROUP BY – group data

10. COUNT / SUM / AVG – summarize data

A Beginner's Project: Analyzing Sales Data with Basic SQL

Sample Sales table:

+----+----------+--------+
| ID | Product  | Amount |
+----+----------+--------+
| 1  | Laptop   | 1000   |
| 2  | Phone    | 500    |
| 3  | Laptop   | 800    |
+----+----------+--------+

Example: Find total sales per product:

SELECT Product, SUM(Amount) AS TotalSales
FROM Sales
GROUP BY Product;

Result:

+---------+------------+
| Product | TotalSales |
+---------+------------+
| Laptop  | 1800       |
| Phone   | 500        |
+---------+------------+

Common SQL Mistakes and How to Avoid Them

• Forgetting the WHERE clause when updating or deleting (can change all rows!).

• Using SELECT * instead of selecting only needed columns.

• Forgetting to add a PRIMARY KEY, leading to duplicate data.

• Mixing up WHERE vs. HAVING.

Putting It All Together: A Comprehensive SQL Fundamentals Review

By now, you’ve learned:

• How to build a table and insert data

• How to query with SELECT, WHERE, ORDER BY

• How to modify data with UPDATE and DELETE

• How to combine tables with JOIN

• How to summarize data with GROUP BY

These are the core SQL fundamentals every beginner should master.

✅ Pro Tip

When practicing SQL, always create small sample projects (like a customer or sales database). This makes learning fun, practical, and much easier to remember compared to just memorizing commands.