Do derived tables require an alias in every SQL dialect?

MySQL and PostgreSQL both raise a syntax error on an unaliased derived table in FROM; SQL Server and SQLite are more lenient, but every major style guide recommends an explicit alias regardless, since an unnamed subquery is hard to reference and hard to read.

Should a subquery go on one line or be broken up?

A short scalar subquery in a SELECT list — a single COUNT() or MAX() — usually reads fine on one line. A subquery with its own WHERE, JOIN, or GROUP BY should almost always be broken onto multiple lines and indented, the same as any SELECT of that size would be.

What's the difference between a correlated and uncorrelated subquery?

An uncorrelated subquery runs once, independent of the outer query. A correlated subquery references a column from the outer query in its own WHERE clause, so conceptually it re-runs once per outer row — worth flagging with a clear alias or comment since it isn't visible from formatting alone.

When should I use a CTE instead of a subquery?

Once a subquery is referenced more than once, nested more than one or two levels deep, or needs its own name to be understood, a CTE (WITH clause) almost always reads better — it names the intermediate result once at the top instead of burying it inline.

Does subquery formatting affect query performance?

No — indentation, alias placement, and line breaks have zero effect on the query plan; formatting is purely for human readability. Performance depends on the query's actual structure and indexes, not how it's laid out on the page.

SQL Formatting

How to Format SQL Subqueries and Derived Tables

By Sharon Ben-Moshe · August 8, 2026 · 2 min read

Sharon Ben-Moshe is the founder of sqlfmt, a browser-based SQL formatter and validator with misspelled-keyword suggestions across PostgreSQL, MySQL, SQLite, SQL Server, and BigQuery.

A subquery buried inline in a WHERE clause or FROM list is unreadable the moment it grows past one line. Here's how to indent, align, and alias nested SELECTs so the outer query's structure stays visible.

Quick answer

A readable subquery is indented one level deeper than the keyword that introduces it, wrapped in its own parentheses on their own lines, and — when used in a FROM clause — always given an explicit alias placed right after the closing parenthesis, so the outer query's structure stays visible without unwinding the nested SELECT first.

How to Format SQL Subqueries and Derived Tables

Quick answer

FAQs

Do derived tables require an alias in every SQL dialect?

Should a subquery go on one line or be broken up?

What's the difference between a correlated and uncorrelated subquery?

When should I use a CTE instead of a subquery?

Does subquery formatting affect query performance?

How to Format SQL CREATE TABLE Statements

How to Format SQL INSERT, UPDATE, and DELETE Statements

How to Format SQL Stored Procedures and Functions

Key takeaways

Subqueries in WHERE

Derived tables in FROM need an alias

Scalar subqueries in the SELECT list

Correlated vs uncorrelated: does it change the formatting?

When a subquery should become a CTE instead

Quick answer

FAQs

Do derived tables require an alias in every SQL dialect?

Should a subquery go on one line or be broken up?

What's the difference between a correlated and uncorrelated subquery?

When should I use a CTE instead of a subquery?

Does subquery formatting affect query performance?

Keep reading

How to Format SQL CREATE TABLE Statements

How to Format SQL INSERT, UPDATE, and DELETE Statements

How to Format SQL Stored Procedures and Functions

Key takeaways

Subqueries in WHERE

Derived tables in FROM need an alias

Scalar subqueries in the SELECT list

Correlated vs uncorrelated: does it change the formatting?

When a subquery should become a CTE instead

Related reading