In this issue, SQL_Parser will implement a framework of bison and flex, which can work togother, bison and flex should be pure which can be reentrant.

High Level Design

I implement the framework according to the book <<flex & bison>>.

Fulfill the file scan.l to support all lexcial.
SQL_Parser's lex scanner should support the following regular expression:

1. Identifier
2. SQL Keywork
3. Operators (+,-,*,/)
4. Interger(Decimal, Oct, Hex)
5. FLOAT
6. String(single quote, double quote)
7. BOOL
8. Comment
9. Spaces( , \t, \n)
10. Multi-byte word(utf8 and so on)

SQL Parser can be run in multi-thread, so the mm should be implement according TLS(Thread Local Store).

SQL Parser need manage memory itself for performance