Exploring Subquery Alternatives: Understanding and Using CTE

Early in my SQL journey, subqueries were my go-to solution for tackling complex problems. They seemed like a simple and intuitive way to nest one query inside another to get the job done. However, as my queries grew more complex, this approach quickly became overwhelming. Subqueries started to feel messy—hard to read, challenging to maintain, and sometimes frustratingly slow. Debugging deeply nested queries, in particular, was a headache. Moreover, at my current workplace, we do not use any ORM tools—instead, we rely entirely on raw SQL queries. This hands-on approach gave me a deeper understanding of SQL but also made the limitations of subqueries even more apparent. Managing intricate logic and transforming data with raw SQL often felt cumbersome. That’s when a colleague introduced me to Common Table Expressions (CTEs). Intrigued, I decided to give them a shot. It turns out that subqueries are not the only way to solve complex nested query problems. In this article, I’ll share what I’ve explored about subqueries and CTEs, using a case study from my own experience to highlight their differences. Let’s dive in! Subquery Subqueries are queries nested within another SQL query, often used to perform intermediate calculations or data filtering. They are enclosed within parentheses and can be used in SELECT, WHERE, or FROM clauses. SELECT column1, column2 FROM table_name WHERE column1 IN ( SELECT column1 FROM another_table WHERE condition ); CTE Common Table Expressions (CTEs) are temporary named result sets defined within a SQL statement using the WITH keyword. They simplify complex queries by breaking them into smaller, reusable components, improving readability and maintainability. WITH cte_name AS ( SELECT column1, column2 FROM table_name WHERE condition ) SELECT * FROM cte_name WHERE other_condition; CASE STUDY

Feb 10, 2025 - 13:32

Exploring Subquery Alternatives: Understanding and Using CTE

Early in my SQL journey, subqueries were my go-to solution for tackling complex problems. They seemed like a simple and intuitive way to nest one query inside another to get the job done. However, as my queries grew more complex, this approach quickly became overwhelming. Subqueries started to feel messy—hard to read, challenging to maintain, and sometimes frustratingly slow. Debugging deeply nested queries, in particular, was a headache.

Moreover, at my current workplace, we do not use any ORM tools—instead, we rely entirely on raw SQL queries. This hands-on approach gave me a deeper understanding of SQL but also made the limitations of subqueries even more apparent. Managing intricate logic and transforming data with raw SQL often felt cumbersome. That’s when a colleague introduced me to Common Table Expressions (CTEs). Intrigued, I decided to give them a shot. It turns out that subqueries are not the only way to solve complex nested query problems.

In this article, I’ll share what I’ve explored about subqueries and CTEs, using a case study from my own experience to highlight their differences. Let’s dive in!

Subquery

Subqueries are queries nested within another SQL query, often used to perform intermediate calculations or data filtering. They are enclosed within parentheses and can be used in SELECT, WHERE, or FROM clauses.

SELECT column1, column2
FROM table_name
WHERE column1 IN (
    SELECT column1
    FROM another_table
    WHERE condition
);

CTE

Common Table Expressions (CTEs) are temporary named result sets defined within a SQL statement using the WITH keyword. They simplify complex queries by breaking them into smaller, reusable components, improving readability and maintainability.

WITH cte_name AS (
    SELECT column1, column2
    FROM table_name
    WHERE condition
)
SELECT *
FROM cte_name
WHERE other_condition;