1. Missing or Misplaced Semicolons

The Mistake:

SELECT * FROM users  
UPDATE users SET status = 'active' -- Missing semicolon

Error: Syntax error near 'UPDATE'

The Fix:

SELECT * FROM users;  
UPDATE users SET status = 'active'

AI2sql Tip: The AI automatically adds semicolons when generating queries.

2. Using = Instead of IS NULL for Null Checks

The Mistake:

SELECT * FROM orders WHERE discount = NULL

Error: Returns zero rows (NULL isn’t comparable with =).

The Fix:

SELECT * FROM orders WHERE discount IS NULL

AI2sql Tip: Describe your goal (“Find orders with no discount”) to get correct syntax.

3. Forgetting GROUP BY with Aggregate Functions

The Mistake:

SELECT department, AVG(salary) FROM

Error: Column 'employees.department' must appear in GROUP BY

The Fix:

SELECT department, AVG(salary)
FROM employees
GROUP BY

AI2sql Hack: Ask, “Show average salary by department” to auto-generate GROUP BY logic.

4. Unintentional Cartesian Products (Cross Joins)

The Mistake:

SELECT * FROM customers, orders; -- No JOIN condition

Result: Millions of rows!

The Fix:

SELECT *
FROM customers
JOIN orders ON

AI2sql Rescue: Describe relationships (“Join customers and orders”) to get proper JOIN clauses.

5. Case Sensitivity in String Comparisons

The Mistake:

SELECT * FROM products WHERE name = 'laptop'; -- Misses 'Laptop' or 'LAPTOP'

The Fix:

SELECT * FROM products WHERE LOWER(name) = 'laptop';
-- OR use case-insensitive collation

AI2sql Insight: It auto-suggests case-handling functions for text searches.

6. Mismatched Data Types

The Mistake:

SELECT * FROM logs WHERE date = '2024-02-30'; -- Invalid date

Error: Invalid datetime format

The Fix:

SELECT * FROM logs WHERE date = '2024-02-28'

AI2sql Bonus: It validates date/number formats during query generation.

7. Overusing SELECT

The Mistake:

SELECT * FROM 10m_row_table; -- Slows performance

The Fix:

SELECT id, name, email FROM users; -- Be specific!

AI2sql Advantage: Translates “Get emails from users” into optimized SELECT statements.

8. Nested Subquery Returning Multiple Rows

The Mistake:

SELECT name FROM products
WHERE price = (SELECT MAX(price) FROM products GROUP BY category)

Error: Subquery returned more than 1 row

The Fix:

SELECT name FROM products
WHERE price IN (SELECT MAX(price) FROM products GROUP BY category)

AI2sql Help: It detects multi-row subqueries and suggests IN or EXISTS.

9. Incorrect ORDER BY Position

The Mistake:

SELECT name, department FROM employees
ORDER BY 3; -- Invalid column index

Error: Invalid column index 3

The Fix:

SELECT name, department, hire_date FROM employees
ORDER BY 3; -- Refers to hire_date

AI2sql Guardrail: The AI avoids positional references for safer sorting.

10. SQL Injection Vulnerabilities

The Mistake:

query = f"SELECT * FROM users WHERE id = {user_input}"

Risk: Hackers can inject malicious code via user_input.

The Fix:

query = "SELECT * FROM users WHERE id = %s"
cursor.execute(query, (user_input,))

AI2sql Security: Generates parameterized queries for Python/JS/PHP integrations.

How AI2sql Prevents These Mistakes

1. Syntax Autocorrect: Fixes missing commas/semicolons in real-time.

2. Type Checking: Flags mismatched data types (dates vs strings).

3. Query Optimization: Recommends indexed columns and avoids SELECT *.

4. Security: Promotes parameterization to block injections.

Try This with AI2sql:

“Show inactive users who joined before 2023, sorted by registration date.”
The AI generates:

SELECT username, email, joined_at
FROM users
WHERE status = 'inactive' AND joined_at < '2023-01-01'
ORDER BY joined_at DESC

Conclusion

Even seasoned developers make SQL mistakes—but tools like AI2sql act as your 24/7 code reviewer. By catching syntax errors, optimizing queries, and teaching best practices, you’ll spend less time debugging and more time delivering insights.

Fix Errors Faster: Generate Error-Free SQL Now