SQL Formatter

An SQL Formatter (or "Beautifier") is a syntactic analysis utility used to transform raw, unreadable database queries into structured, indented code blocks. This tool is essential for database administrators, backend developers, and data analysts debugging complex JOINs, reviewing stored procedures, or preparing queries for documentation.

Implementation & Processing Pipeline

The formatting engine handles SQL syntax through a multi-stage tokenization pipeline:

1. Lexical Analysis: The tool breaks the raw string into "Tokens" (Keywords, Identifiers, Literals, Operators).
2. Dialect Recognition: It identifies specific syntax rules (e.g., Backticks for MySQL vs Quotes for PostgreSQL ").
3. Indentation Logic: The engine applies standard "River" indentation:
   • Keywords: Aligned right (e.g., SELECT, FROM, WHERE).
   • Columns/Conditions: Indented left.
4. Case Standardization: It automatically converts recognized keywords to UPPERCASE (e.g., select -> SELECT) for readability.

How It's Tested

We test the formatter against complex queries to ensure it improves readability without breaking logic.

1. The "Minified" Check:
   • Action: Format SELECT * FROM users WHERE id=1.
   • Expected:

     SELECT *
     FROM users
     WHERE id = 1
     

2. The "Nested Subquery" Test:
   • Action: Format a query with a sub-SELECT three levels deep.
   • Expected: Each level must be indented deeper (2 or 4 spaces) to visually show the hierarchy.
3. The "Dialect" Verification:
   • Action: select "PostgreSQL" mode and format text with LIMIT and OFFSET.
   • Expected: The formatter respects the specific syntax of the chosen dialect.
4. The "Safety" Check:
   • Action: Format a query with syntax errors (e.g., missing FROM).
   • Expected: The tool should attempt to format the known tokens or fail gracefully/warn, not crash.

Technical specifications and standard documents are available at the ISO Official SQL Standard page, the PostgreSQL Official Documentation, and the MySQL Reference Manual.