day 04 模拟mysql实现 增删改查

环境：win7系统、anaconda3 和 pycharm

要想实现增删改查的命令，首先对命令进行分析，对命令进行分析，提取有用的信息

比如：数据表、where条件、要显示的字段

对命令进行分割（split(' ')）

select * from user where name = '李云龙'

sql = "select *   from user where name = '李云龙'"
sql_list = sql.strip().split(' ') #以空格为分隔符
print(sql_list)
res = []
for i in sql_list: #遍历列表，去除空白元素
    if i:
        res.append(i)
print(res)
sql_list = res

　　

sql_list = ['select', '*', 'from', 'user', 'where', 'name', '=', "'李云龙'"]

if 'from' in sql_list:
　　from_id = sql_list('from'） #得到from 在sql_list 中的索引号
　　table = sql_list[from_id + 1]
if 'where' in sql_list:
　　where_list = sql_list[-3:] # 得到where_list

def where(table,where_list):
    """
    :param table: 数据表
    :param where_list: 筛选条件列表
    :return: 
    """
    title = "id,name,age,phone,dept,enroll_date"
    fh = open(table,'r',encoding='utf8')
    res = []
    for line in fh:
        dic = dict(zip(title.split(','),line.split(','))) #利用zip 函数 定义字典
        exp_k,opt,exp_v = where_list
        # print(opt == 'like')
        if opt == "=":
            opt = '%s='%where_list[1]
        if dic[exp_k].isdigit():
            dic_v = int(dic[exp_k])
            exp_v = int(exp_v)
        else:
            dic_v = "'%s'"%dic[exp_k]
        if opt != 'like':
            exp = eval('%s%s%s'%(dic_v,opt,exp_v))
            if exp:
                res.append(line)
        else:
            if exp_v in dic_v:
                print('exp_v %s,dic_v:  %s'%(exp_v,dic_v))
                res.append(line)
    # print('符合条件的数据行：%s'%res)
    return res

　　需要什么，就想法利用字典或列表的属性得到他，然后测试是否可行！

这些都是按照正常思路设计的，如果你要剑走偏锋报错了，我就不负责了，嘿嘿

下面是完整的实例：

import os

def rename_file(table,newfile):# 实现旧表的删除，新表的重命名
    os.remove(table)
    os.renames(newfile,table)

def insert(sql_list):
    # insert into user values 李云龙,35,1889922334,2017-05-05
    table = sql_list[2]
    info = sql_list[-1]
    with open(table,'r+',encoding='utf8') as fh:
        res = []
        for line in fh:
            if len(line) != 0:
                res.append(line)
        last_line = res[-1]
        id  = int(last_line.strip().split(',')[0])
        new_id = id + 1
        new_line = '%s,%s
'%(str(new_id),info)
        print(new_line)
        fh.write(new_line)
        fh.close()
        print('成功写入：%s'%info)

def delete(sql_list):
    #delete from user where name like '李'
    table = sql_list[2]
    if 'where' not in sql_list:
        with open(table,'r',encoding='utf8') as f:
            result = f.readlines()
    else:
        where_list = sql_list[-3:]
        result = where(table,where_list)
        print('即将删除：%s'%result)
    new_file = 'new_file'
    with open(table,'r',encoding='utf8') as f,
            open(new_file,'w',encoding='utf8') as new_f:
        for line in f:
            if line not in result:
                new_f.write(line)
                new_f.flush()


def update(sql_list):
    # update user set dept = 'sa' where age < 18
    title = "id,name,age,phone,dept,enroll_date"
    up_set = sql_list[3:6]
    print(up_set)
    table = sql_list[1]
    new_file = 'new_file'
    if 'where' not in sql_list:
        print('update 语法错误！')
        exit()
    else:
        where_list = sql_list[-3:]
        with open(table,'r',encoding='utf8') as f,
            open(new_file,'w',encoding='utf8') as new_f:
            res = where(table,where_list)
            print(res)
            if res:
                for line in f:
                    if line in res:
                        dic = dict(zip(title.strip().split(','),line.strip().split(',')))
                        dic[up_set[0]] = up_set[-1]
                        new_line = '%s,%s,%s,%s,%s,%s
'%(dic["id"],dic["name"],dic["age"],dic['phone'],dic["dept"],dic["enroll_date"])
                        print("newline'",new_line)
                        new_f.write(new_line)
                        new_f.flush()
                    else:
                        new_f.write(line)
                        new_f.flush()


def select(sql_list):
    #select  * from user where dept = IT
    from_id = sql_list.index('from')
    fields = sql_list[1:from_id] # 得到需要筛选的字段
    table = sql_list[from_id+1]
    if 'where' not in sql_list:
        fh = open(table,'r',encoding='utf8')
        res = fh.readlines()
        if res:
            res = search(fields,res)
            for i in res:
                print(i)
        else:
            print('没有结果')
    else:
        where_list = sql_list[-3:]
        res = where(table,where_list)
        if res:
            res = search(fields,res)
            for i in res:
                print(i)
        else:
            print('没有结果')

def search(field,res):
    title = "id,name,age,phone,dept,enroll_date"
    sea_res = []
    for line in res:
        #利用 zip 函数 得到 数据行的字典
        dic = dict(zip(title.strip().split(','),line.strip().split(',')))
        if len(field) == 1:
            if field[0] == '*':
                return res
            else:
                sea_res.append(dic[field[0]])
        else:
            r_l = []
            for i in field:
                r_l.append(dic[i].strip())
            sea_res.append(r_l)
    return sea_res


def where(table,where_list):
    """
    :param table: 数据表
    :param where_list: 筛选条件列表
    :return: 
    """
    title = "id,name,age,phone,dept,enroll_date"
    fh = open(table,'r',encoding='utf8')
    res = []
    for line in fh:
        dic = dict(zip(title.split(','),line.split(',')))
        exp_k,opt,exp_v = where_list
        # print(opt == 'like')
        if opt == "=":
            opt = '%s='%where_list[1]
        if dic[exp_k].isdigit():
            dic_v = int(dic[exp_k])
            exp_v = int(exp_v)
        else:
            dic_v = "'%s'"%dic[exp_k]
        if opt != 'like':
            exp = eval('%s%s%s'%(dic_v,opt,exp_v))
            if exp:
                res.append(line)
        else:
            if exp_v in dic_v:
                print('exp_v %s,dic_v:  %s'%(exp_v,dic_v))
                res.append(line)
    # print('符合条件的数据行：%s'%res)
    return res

test_sql = """
# insert into user values 李云龙,32,1999883771,IT,2017-07-08
# delete from user where name = '李云龙'
# delete from user where name like '李'
# update user set dept = 运维 where name = '李云龙'
# select * from user where dept = 'IT'
# select name age from user where dept = 'IT'
# select * from user where enroll_date like 2013
# select name age from user where age > 22
# select id name age phone from user where age > 20
# select * from user name like '李'
"""
if __name__ == "__main__":
    print(test_sql)
    print('测试命令如上：')
    while True:
        print('字段名称：33[33mid,name,age,phone,dept,enroll_date33[0m')
        sql = input('sql command >').strip()
        if sql =='exit':
            exit()
        if len(sql) == 0:
            continue
        sql_list = sql.strip().split(' ')
        print(sql_list)
        res = []
        for i in sql_list:
            if i:
                res.append(i)
        sql_list = res
        func = sql_list[0]
        dic_sql = {'insert':insert,
                   'delete':delete,
                   'update':update,
                   'select':select,}

        if func in dic_sql:
            res = dic_sql[func](sql_list)
            print(res)
        else:
            print('不能识别的sql 命令')
            continue

　　慢慢来，整理思路，回头再看看视频，会有柳暗花明的感觉，加油！