SQL lex files:

sql/sql_lex.h、sql/lex_token.h、sql/lex.h、sql/lex_symbol.h

sql/gen_lex_token.cc、sql/sql_lex.cc

SQL grammar parser file:

sql/sql_yacc.yy、sql/sql_yacc.cc、sql/sql_yacc.h

SQL hint grammar parser file:

sql/sql_hints.yy、sql/sql_hints.yy.cc

mysql use bison (lex/yacc) to token sql statement and parse it, take sql_yacc.yy for example, it is main file contains all parse sql rules.