解决出现Incorrect integer value: '' for column 'id' at row 1的问题

# -*- coding: utf-8 -*- 
import MySQLdb 
 
class Mysql: 
  conn = ''  
  cursor = '' 
 
  def __init__(self, host='localhost', usr='blogtest', password='111222', db='blogtest'): 
    try: 
      self.conn = MySQLdb.connect(host, usr, password, db) 
    except Exception, e: 
      print e 
    self.cursor = self.conn.cursor() 
    #self.query('SET NAME %s ' % charset) 
 
 
  def query(self, sql): 
    self.cursor.execute(sql) 
 
  def show(self): 
    return self.cursor.fetchall() 
 
  def db_insert(self,sql): 
    self.cursor.execute(sql) 
    self.conn.commit() 
 
  def __del__(self): 
    self.cursor.close() 
    self.conn.close() 
 
if __name__ == '__main__': 
  mysql = Mysql() 
  mysql.db_insert("insert into userinfo values(NULL,'sven','111222','sven@qq.com','1')") 
  mysql.query('SELECT * FROM userinfo') 
  data = mysql.show() 
  for x in data: 
    print x