SQLGlot: SQL Parser, Transpiler, and Optimizer

Warnings

• gotcha Failing to specify the `read` (source) or `write` (target) dialect during `parse_one` or `transpile` calls can lead to `ParseError` or incorrect output. SQLGlot defaults to its 'SQLGlot dialect', which is a superset, if not specified.
  Fix: Always specify `read='your_source_dialect'` when parsing and `write='your_target_dialect'` when transpiling for accurate results (e.g., `parse_one(sql, read='spark')`).
• gotcha SQLGlot strictly parses valid SQL. It will raise a `ParseError` if the SQL string contains non-SQL constructs like templating variables (e.g., `{{parameter}}`) or invalid syntax (e.g., unquoted timestamps in some contexts).
  Fix: Pre-render or interpolate any non-SQL templating variables before passing the SQL string to SQLGlot. Ensure all SQL literals, especially timestamps, are correctly quoted according to SQL standards.
• breaking SQLGlot's versioning strategy indicates that MINOR version increments (e.g., 29.x to 30.x) can introduce backwards-incompatible fixes or feature additions. Be mindful of minor version bumps during upgrades.
  Fix: Refer to the official changelog or release notes for each minor version upgrade to identify potential breaking changes and necessary code adjustments. Test thoroughly before deploying new minor versions.
• gotcha While SQLGlot is comprehensive, transpilation across all possible dialect pairs and inputs is an 'incremental' problem. Some specific dialect conversions may have limitations or ongoing improvements.
  Fix: If encountering unexpected transpilation behavior for specific dialect features, consult the SQLGlot documentation, raise an issue on GitHub, or consider contributing a fix.
• gotcha Parsing SQL queries with column names or identifiers using non-standard quoting (e.g., backticks as often used by LLMs) can lead to `ParseError`.
  Fix: As a workaround, replace non-standard cross-quotes with standard double quotes (`"`) before parsing, or ensure the input SQL conforms to a supported dialect's quoting conventions.

Install

• pip install sqlglot Core library
• pip install "sqlglot[c]" With C extensions (if available)
• pip install "sqlglot[rs]" With Rust tokenizer (for performance)

Imports

• parse_one

  from sqlglot import parse_one

  Commonly imported directly for convenience; the root module also provides it.
• transpile

  from sqlglot import transpile

  Commonly imported directly for convenience; the root module also provides it.
• exp

  from sqlglot import exp

  The `exp` submodule contains all expression types for AST manipulation and is typically imported directly from the root `sqlglot` module now.

Quickstart

This quickstart demonstrates basic SQL parsing and cross-dialect transpilation. The `parse_one` function converts a SQL string into an Abstract Syntax Tree (AST), while `transpile` converts SQL between specified dialects. It also shows a common pattern for transforming MySQL-specific functions to BigQuery equivalents.

from sqlglot import parse_one, transpile

# Parse a SQL query (defaults to SQLGlot dialect if 'read' is not specified)
sql_query = "SELECT id, name FROM users WHERE age > 18"
expression = parse_one(sql_query)
print(f"Parsed Expression: {expression}")

# Transpile from MySQL to BigQuery
mysql_query = "SELECT IFNULL(employee_name, 'Unknown') AS employee_status FROM employees;"
bigquery_query = transpile(mysql_query, read="mysql", write="bigquery")[0]
print(f"Transpiled to BigQuery: {bigquery_query}")

# Further manipulation of the AST is possible with `expression` object
# E.g., print(expression.find_all(exp.Column))