I've just added mysql_sql.y to https://mingodad.github.io/parsertl-playground/playground/ an online Yacc/Lex compatible editor/tester (select Matrixone MySql (be patient)(partially working) from examples then click Parse to see a parser tree for the contents in Input source editor).

I hope it can help debug/develop/document mysql_sql.y.

There is also other SQL like grammars:

• AlaSQL parser
• ArangoDB AQL parser
• CG-CQL-author parser
• Mysql parser
• OctoSQL parser
• Postgresql parser
• SQLite3 parser
• TDengine SQL
• Tidb SQL
• Tradofion SQL
• Vitess SQL

Any feedback is welcome !