错误现象：
sql_lex.cc: In function `void lex_init()':
sql_lex.cc:85: `symbols' undeclared (first use this function)
sql_lex.cc:85: (Each undeclared identifier is reported only once
sql_lex.cc:85: for each function it appears in.)
sql_lex.cc:87: `sql_functions' undeclared (first use this function)
sql_lex.cc: In function `int find_keyword(LEX *, unsigned int, bool)':
sql_lex.cc:171: implicit declaration of function `int get_hash_symbol(...)'
sql_lex.cc:171: initialization to `SYMBOL *' from `int' lacks a cast
解决办法：
cd sql
make gen_lex_hash
./gen_lex_hash > lex_hash.h
make
