Format and structure SQL queries for better readability

SQL Formatter — Readable Query Structure for PostgreSQL, MySQL, SQLite, and T-SQL

SQL queries generated by ORMs, extracted from application logs, or exported from database monitoring tools arrive as long, unformatted strings that are nearly impossible to read or debug. A query like SELECT u.id,u.name,o.total FROM users u INNER JOIN orders o ON u.id=o.user_id WHERE o.status='completed' AND o.created_at > '2024-01-01' GROUP BY u.id,u.name ORDER BY o.total DESC LIMIT 100 contains all the information needed to understand the query's logic, but that logic is invisible without formatting. Formatted with proper indentation, keyword capitalization, and aligned clauses, the same query's structure — which tables, what joins, which filters, how grouping and sorting work — becomes immediately readable for debugging, optimization, and documentation.

SQL dialect differences between database systems affect how queries should be formatted and what syntax is valid. PostgreSQL uses double-quotes for identifiers and supports advanced features like window functions, CTEs, and array operations that MySQL handles differently or not at all. MySQL uses backticks for identifier quoting and has its own dialect for features like LIMIT with OFFSET. SQL Server (T-SQL) uses square brackets for identifiers and has proprietary syntax for features like TOP instead of LIMIT. SQLite has a permissive parser that accepts some syntax other databases reject. The SQL formatter applies dialect-specific rules when a target database is specified — quoting identifiers correctly, formatting dialect-specific clauses appropriately, and flagging syntax that may not be portable to other systems.

Query optimization awareness in SQL formatting goes beyond style — formatting choices reveal query structure that affects performance. Breaking a complex WHERE clause onto separate lines with each condition on its own line makes it immediately visible whether indexes on the filtered columns are likely to be used. Formatting JOIN conditions explicitly — ON table_a.foreign_key = table_b.primary_key — makes the join relationship readable and distinguishes intended join columns from accidental Cartesian products. Formatting CTEs (Common Table Expressions) with WITH clauses on separate lines makes the logical decomposition of a complex query into named subqueries visible, which is both more readable and often more optimizable than deeply nested subqueries. The formatter applies these structural formatting decisions consistently across all dialect options.