Just took a quick look, and it seams like the parser is hand written which is great, but you probably want to build a lexer and parser based on the BNF grammar take a look at how I do it here https://github.com/elixir-dbvisor/sql/tree/main/lib and do conformance testing with https://github.com/elliotchance/sqltest
Ibis has sqlglot for parsing and rewriting SQL query graphs; and there's sql-to-ibis: https://github.com/ibis-project/ibis/issues/9529
sqlglot: https://github.com/tobymao/sqlglot :
> SQLGlot is a no-dependency SQL parser, transpiler, optimizer, and engine [written in Python]. It can be used to format SQL or translate between 24 different dialects like DuckDB, Presto / Trino, Spark / Databricks, Snowflake, and BigQuery. It aims to read a wide variety of SQL inputs and output syntactically and semantically correct SQL in the targeted dialects.
You can google SQL grammar. But here is the 2025: https://standards.iso.org/iso-iec/9075/-2/ed-6/en/
Thanks, do you have a reference for SQL grammar - I've had no success finding an official source.