Learning SQL One Question at a Time: What I Asked and Understood

Introduction

Today, I didn’t just “study SQL.” I struggled with it, debugged it, rephrased it, and kept asking questions.
Each time something didn’t work, it pushed me to think more clearly — and that’s exactly how I learned.

This post is a log of my real questions and the understanding I built through them.

---

1. “Why does SQL give an error if I use ORDER BY twice?”

-- Incorrect
ORDER BY title DESC
ORDER BY rental_rate DESC;

The problem: SQL only allows one ORDER BY clause. You must separate multiple sort conditions with commas.
Fix:

ORDER BY title DESC, rental_rate DESC;

---

2. “How do I find words that are exactly 5 letters long?”

Answer: Use CHAR_LENGTH() or LENGTH() to filter based on string length.

SELECT * FROM users WHERE CHAR_LENGTH(username) = 5;

---

3. “My date is in Y-M-D format. How do I filter by year?”

Answer: Use the YEAR() function to extract just the year from a date column.

SELECT * FROM orders WHERE YEAR(order_date) = 2023;

---

4. “Why do I get an error when I use HAVING?”

The issue: HAVING must follow GROUP BY and only works on aggregated values.
Use WHERE to filter before grouping, and HAVING to filter after.

SELECT customer_id, COUNT(*) AS order_count
FROM orders
GROUP BY customer_id
HAVING order_count >= 5;

---

5. “How do I load a .sql file into MySQL using DBeaver?”

Answer:

• In DBeaver, connect to your database
• Right-click the connection → Tools > Execute SQL Script
• Choose your .sql file and run it

---

What I Realized

Today wasn’t about learning new SQL commands — it was about understanding how to think in SQL:

• Why the order of clauses matters
• Why small syntax choices break whole queries
• Why it’s better to ask lots of tiny questions than to memorize templates

---

What I Want to Do Next

• Practice writing grouped queries with multiple conditions
• Learn to debug long SQL blocks by breaking them into parts
• Start using aliases more clearly to improve readability
• Try creating subqueries with IN, EXISTS, and nested SELECTs

---

SQL isn’t just a query language — it’s a way of thinking about logic, filtering, and structure.
And today, I got better at thinking like that — one question at a time.