**Performance:**

- Put most selective conditions first

- Use indexes on filtered columns

- Avoid functions on indexed columns

- OR conditions can prevent index usage

- Consider UNION for complex OR logic

Put selective conditions first

Index columns in WHERE clause

Avoid functions on indexed columns

Consider UNION for complex OR logic

Test query plans for optimization

Forgetting parentheses with mixed AND/OR

Misunderstanding operator precedence

Creating impossible conditions (AND with contradictions)

Not testing edge cases

Overly complex logic (hard to maintain)