利用python模拟数据库对表中信息的增删查改

• 要求：

  由于只有一个表，所以只能在这个表中进行操作
  可以进行对员工信息表的内容进行增、删、查、改
  增： INSERT VALUES(值1，值2，...)
  查： SELECT * WHERE age > 20
  改： SET name = 'sb' WHERE id = 1
  删： DELETE WHERE id = 1
  

• 使用了re正则模块，进行字符串的匹配，增加容错能力。

  import re
  import os
  import sys
  BASE_PATH = os.path.dirname(__file__)
  sys.path.append(os.path.dirname(BASE_PATH))
  from core import home_page
  from config import settings
  
  exp1 = 'select name, age where age>22  '
  exp2 = 'select * where job=IT  '
  exp3 = 'select * where phone like 133'
  
  def func_title(li,r1,title):
      '''为查询结果添加列名'''         # 重复率太高了
      l2 = []
      if ',' in r1:  # 多个列
          l1 = r1.strip().split(',')
          for j in l1:
              l2.append(j)
          li.append(l2)
          return li
      elif '*' in r1:  # 所有列
          for j in title:
              l2.append(j.strip())
          li.append(l2)
          return li
      else:   # 一个列
          l2.append(r1)
          li.append(l2)
          return li
  
  def filter_sub(li,r1,dic_f):
      '''对于列名的处理有三种情况：单个列名，多个列名，所有列名'''
      if ',' in r1:
          l1 = r1.strip().split(',')
          for j in l1:
              li.append(dic_f[j.strip()])
          return li
      elif '*' in r1:
          for j in dic_f.values():
              li.append(j.strip())
          return li
      else:
          li.append(dic_f[r1])
          return li
  
  def func_filter(li,dic_f,r1,r2,r3,r4):
      '''where条件后的判断方式 > < , = '''
      if r3 == '>':
          if float(dic_f[r2]) > float(r4):
              return filter_sub(li, r1, dic_f)
          else:
              return li
  
      elif r3 == '<':
          if float(dic_f[r2]) < float(r4):
              return filter_sub(li, r1, dic_f)
          else:
              return li
      elif r3 == '=':
          #     # 先确定 where条件后的判断方式 > < =  ，接下来确定 该项留不留下,做成函数，返回True or False，   第三步：该项输出的内容
          if dic_f[r2] == r4:
              return filter_sub(li,r1,dic_f)
          else:
              return li
  
      elif r3 == 'like':
          if r4 in dic_f[r2] :
              return filter_sub(li, r1, dic_f)
          else:
              return li
  
  def func_select(exp):
      '''
      模拟数据库查询select操作，支持：大于小于等于，还要支持模糊查找。
      '''
      exp = exp.strip()
      pa = '[sS][eE][lL][eE][cC][tT]s+(w+(?:,s*w+)*|[*])s+(?:froms+d+s+)?[wW][hH][eE][rR][eE]s+(w+)(?:s*([><])s*|s*([=])s*|s+([lL][iI][kK][eE])s+)(w+)s*$'
      ret = re.match(pa, exp)
      if ret:
          r1 = ret.group(1).strip()        # name, age   # 最终显示的项
          r2 = ret.group(2).strip()        # 比较的条件1
          r3 = list(filter(lambda x:x,[ret.group(3),ret.group(4),ret.group(5)]))[0].strip()   #ret.group(3) ，4，5 分别为 >< , = , like。从中选一个当作r3
          r4 = ret.group(6).strip()        ## 比较的条件2
          with open(settings.USER_INFO_PATH, encoding='utf-8') as f:
              title = f.readline().strip().split(',')
              li = []
              li = func_title(li,r1,title)
  
              for i in f:
                  l1 = []
                  dic_f = {k: '' for k in title}
                  lis_f = i.strip().split(',')
                  for j, k in zip(dic_f, lis_f):
                      dic_f[j] = k
                  # print(dic_f)
                  l1 = func_filter(l1,dic_f,r1,r2,r3,r4)
                  if l1:li.append(l1)
          if li:
              for i in li:
                  for j in i:
                      print('	'+ j+ '	',end='')
                  print()
  
          else:
              print('信息不存在！')
      else:
          print('查询语句有误')
  
  
  def insert_sub(l1):
      with open(settings.USER_INFO_PATH, encoding='utf-8', mode='r+') as f:
          title = f.readline().strip().split(',')
          # print(title)
          if len(title)>2:
              for i in f:
                  l2 = i.strip()
              l2 = l2.split(',')  # 使用最后一次的id
              if len(l1) + 1 == len(title):
                  content = '
  ' + str(int(l2[0])+1) + ','
                  for i in l1:
                      content = content + i.strip() + ','
                  content = content.strip(',')
                  f.write(content)
                  print('添加成功！')
              else:
                  print('输入的值的数量不对应')
          else:
              print('输入的值的数量不对应')
  
  def func_insert(exp):
      '''模拟数据库inset操作'''
      exp = exp.strip()
      pa = '[iI][nN][sS][eE][rR][tT]s+(?:intos+w+s+)?valuess*[(]s*(w+s*(?:[,，]s*w+s*)*)[)]$'
  
      # 支持两种方式：INSERT INTO 表名称 VALUES (值1, 值2,....)   INSERT INTO table_name (列1, 列2,...) VALUES (值1, 值2,....)
      ret = re.match(pa, exp)
      if ret:
          print(ret.group(0))
          print(ret.group(1))
          r1 = ret.group(1).strip()
          if ',' in r1:
              l1 = r1.split(',')
              # print(l1)
              # 多个元素
              insert_sub(l1)
          else:
              # 单个元素
              insert_sub(r1)
      else:
          print('增加语句有误')
  
  
  def func_modify(exp):
      '''模拟数据库的改操作set'''
      exp = exp.strip()
      pa = "[sS][eE][tT]s+((?:(?:w+)s*=s*'?(?:w+)s+'?)+)s*[wW][hH][eE][rR][eE]s+(id)s*(=)s*(d+)"
      ret = re.match(pa,exp)
      if ret:
          # print(ret.group(1))
          # print(ret.group(2))
          # print(ret.group(3))
          # print(ret.group(4))
          r1 = ret.group(1)       # name = atlas job = ce phone = 1345        name=atlas job=ce phone=1345
          r2 = ret.group(2)       # id
          r3 = ret.group(3)       # =
          r4 = ret.group(4)       # 4
          pa2 = 's*(w+)s*=s*(w+)s*'
          r5 = re.findall(pa2,r1)
          print(r5)
          with open(settings.USER_INFO_PATH, encoding='utf-8')as f1 ,
               open(settings.USER_INFO_PATH+'.swap',encoding='utf-8',mode='w') as  f2 :
                  title = f1.readline().strip().split(',')
                  f2.write(','.join(title)+'
  ')
                  for i in f1:
                      dic_f = {k: '' for k in title}
                      lis_f = i.strip().split(',')
                      for j, k in zip(dic_f, lis_f):
                          dic_f[j] = k
                      if dic_f['id'] == r4:
                          for j in r5:
                              dic_f[j[0]] = j[1]
                          cont = ''
                          for k in dic_f.values():
                              cont = cont + k + ','
                          cont = cont.strip(',')
                          f2.write(cont+'
  ')
                      else:
                          f2.write(i)
                  print('修改成功！')
          os.remove(settings.USER_INFO_PATH)
          os.rename(settings.USER_INFO_PATH+'.swap',settings.USER_INFO_PATH)
  
      else:
          print('SQL语句输入错误！')
  
  
  def func_del(exp):
      '''模拟数据库的删除操作delete'''
      exp = exp.strip()
      pa = 's*[dD][eE][lL][eE][tT][eE]s+[wW][hH][eE][rR][eE]s+ids*=s*(d+)'
      ret = re.match(pa, exp)
      if ret:
          r1 = ret.group(1)  # id = (6) 因为只有一个表，而id是这个表的主键，所以我们把主键默认为id去进行匹配
          print(r1)
          with open(settings.USER_INFO_PATH, encoding='utf-8')as f1, 
                  open(settings.USER_INFO_PATH+'.swap', encoding='utf-8', mode='w') as  f2:
              title = f1.readline().strip().split(',')
              f2.write(','.join(title) + '
  ')
              for i in f1:
                  dic_f = {k: '' for k in title}
                  lis_f = i.strip().split(',')
                  for j, k in zip(dic_f, lis_f):
                      dic_f[j] = k
                  if dic_f['id'] == r1:
                      pass  # 找到待删除的id，就把这条记录丢下。
                  else:
                      f2.write(i)
              print('修改成功！')
          os.remove(settings.USER_INFO_PATH)
          os.rename(settings.USER_INFO_PATH+'.swap', settings.USER_INFO_PATH)
      else:
          print('SQL语句输入错误！')
  
  def run():
      '''程序入口'''
      home_page.home()
      flag = True
      while flag:
          choose = input(' 请输入SQL语句>>> ')
          pat2 = '[iI][nN][sS][eE][rR][tT]'
          if re.findall('[sS][eE][lL][eE][cC][tT]',choose):
              # 执行查询操作
              func_select(choose)
          elif re.findall('[iI][nN][sS][eE][rR][tT]',choose):
              # 执行增加操作
              func_insert(choose)
          elif re.findall('[sS][eE][tT]',choose):
              # 执行修改操作
              func_modify(choose)
          elif re.findall('[dD][eE][lL][eE][tT][eE]',choose):
              # 执行删除操作
              func_del(choose)
          else:
              print('输入的SQL语句有误')
          conti = input('Q/q退出,其他键继续 ')
          print()
          if conti.upper() == 'Q':flag = False
  
  
  
  if __name__ == '__main__':
      run()