Antlr4 grammar for SQL SELECT statement. Overview of syntax located at SYNTAX.md.
You can test this (in Java) by doing:
$ cd grammar
$ java -jar ../antlr-4.10.1-complete.jar Datadocs*.g4 -o out
$ cd out
$ javac Datadocs*.java
$ time java org.antlr.v4.gui.TestRig Datadocs testRoot ../../test/duckdb_legacy.sql