🚀 Mastering SQL: Common Table Expressions (CTEs) vs. Subqueries – Which One Should You Use?

In the world of SQL, we often need to structure complex queries efficiently. Two common approaches are Common Table Expressions (CTEs) and Subqueries. But which one is better?

✅ CTEs (WITH) ✔ Improves readability and code organization. ✔ Allows reuse within the same query. ✔ Makes debugging and maintenance easier. ✔ Can improve performance by avoiding repeated subquery executions.

❌ Subqueries ✔ More compact for simple queries. ✔ Executed inline, sometimes offering better performance. ✔ Requires less code when reuse is unnecessary.

💡 Advanced tip: If a subquery is used multiple times within the same query, consider converting it into a CTE to avoid unnecessary calculations and improve performance.

🔍 Practical example: Find employees who earn above the department average.

🔹 Using a Subquery:

SELECT emp_name, salary  
FROM employees  
WHERE salary > (SELECT AVG(salary) FROM employees);        

🔹 Using a CTE:

WITH avg_salary AS (  
    SELECT AVG(salary) AS avg_sal FROM employees  
)  
SELECT emp_name, salary  
FROM employees, avg_salary  
WHERE salary > avg_salary.avg_sal;        

📌 When to Choose CTEs? ✔ Complex queries with multiple levels. ✔ When the same subquery is used repeatedly. ✔ For better maintenance and readability.

📢 What do you use more often in your daily work: CTEs or Subqueries? Share your thoughts in the comments! 👇