Unformatted SQL is nearly unreadable. A single-line query that's a hundred words long might be perfectly valid but completely unmaintainable. SQL formatting isn't cosmetic — it's functional. Well-formatted SQL is faster to review, easier to debug, and less likely to harbor subtle bugs that hide in dense, unspaced text.
SQL Formatting Standards
There's no ISO standard for SQL formatting, but industry conventions have emerged. The most common style: uppercase keywords (SELECT, FROM, WHERE, JOIN, GROUP BY), each clause on a new line, indented subqueries, and aligned aliases.
The consistent principle: visual hierarchy should reflect logical hierarchy. A WHERE clause with five conditions should be visually structured so you can see each condition independently. JOINs should be indented to show the table relationships. Subqueries should be further indented to show nesting depth.
SQL Dialects: Where They Differ
Standard SQL (SQL-92, SQL-99, SQL:2003) provides the core syntax. Every database extends it in incompatible ways.
MySQL / MariaDB: backtick identifiers, GROUP BY requires all SELECT columns (unless using ANY_VALUE). PostgreSQL: double-quote identifiers, richer set of data types, window functions with extensive syntax. BigQuery: Standard SQL mode with some extensions, array/struct types, UNNEST for flattening. Snowflake: close to standard SQL with proprietary functions like FLATTEN, LATERAL FLATTEN for semi-structured data. Understanding which dialect you're writing for affects both syntax and formatting choices.
CTEs vs Subqueries: Readability Matters
Common Table Expressions (CTEs) — defined with WITH clause — dramatically improve readability for complex queries. A query with three nested subqueries is hard to follow. The same logic expressed as three sequential CTEs reads like prose.
The formatter's job with CTEs: each CTE name is aligned with the WITH keyword, the AS ( keyword starts a new line, the CTE body is indented. The final SELECT from the CTEs reads cleanly. This pattern makes even 200-line SQL queries reviewable.
Formatted SQL isn't just easier to read — it's faster to write, easier to diff in code review, and more likely to reveal logical errors before they reach production. Format before every commit.
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