SQL查询与Python实现-优快云博客

本文详细介绍了如何使用Python实现SQL风格的数据查询，包括条件筛选、字段选择等关键操作，通过具体示例展示了如何从文件中读取数据并进行高效过滤。

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查询语句的实现

def read_file():
    '''读文件'''
    with open('userinfo','r') as f:
        for line in f:
            line_lst = line.strip().split(',')  # ['1','Alex','22','13651054608','IT']
            yield line_lst

def filter_item(col,value,signal):
    '''筛选条件  col='age' 22 >'''   #dic[col] == dic['age'] == 2
    dic = {'id':0,'name':1,'age':2,'phone':3,'job':4}
    correct = []   #存储符合条件的行列表
    for line_lst in read_file():
        #['1','Alex','22','13651054608','IT']   age > 20
        if signal == '>':
            if int(line_lst[dic[col]]) > int(value):
                correct.append(line_lst)
        elif signal == '<':
            if int(line_lst[dic[col]]) < int(value):
                correct.append(line_lst)
        elif signal == '=':
            if line_lst[dic[col]] == value:
                correct.append(line_lst)
        elif signal == 'like':
            if value in line_lst[dic[col]]:
                correct.append(line_lst)
    return correct

def condition_an(con):
    # 分析条件
    # 根据条件中的符号来进行操作: > < = like
    if '>' in con:   # age > 22
        col_name,value = con.split('>')   #age,22
        col_name = col_name.strip()  #'age'
        value = value.strip()        #'22'
        correct = filter_item(col_name,value,'>')  # 筛选出来所有符合条件的项
    elif '<' in con:   # age < 22
        col_name,value = con.split('<')   #age,22
        col_name = col_name.strip()  #'age'
        value = value.strip()        #'22'
        correct = filter_item(col_name,value,'<')  # 筛选出来所有符合条件的项
    elif '=' in con:   # age < 22
        col_name,value = con.split('=')   #age,22
        col_name = col_name.strip()  #'age'
        value = value.strip()        #'22'
        correct = filter_item(col_name,value,'=')  # 筛选出来所有符合条件的项
    elif 'like' in con:   # age < 22
        col_name,value = con.split('like')   #age,22
        col_name = col_name.strip()  #'age'
        value = value.strip()        #'22'
        correct = filter_item(col_name,value,'like')  # 筛选出来所有符合条件的项
    return correct

def show(col,correct):
    # 展示符合条件的行中需要的字段  col = 'name,age,phone,job'   '*'
    dic = {'id': 0, 'name': 1, 'age': 2, 'phone': 3, 'job': 4}
    if '*' == col.strip():
        col_lst = dic.keys()      #[id,name,age,phone,job]
    else:
        col_lst = col.split(',')  #[name,age,phone,job]
    for i in correct:
        #i = ['1', 'Alex', '22', '13651054608', 'IT']
        for col in col_lst:
            print(i[dic[col]],end=' ')
        print()
# exp = input('>>>')
exp = 'select * where phone like 133'
# exp = 'select * where age>22'
col,con = exp.split('where')  # 要显示的列,条件
col = col.replace('select','').strip()
print(col,con)
correct = condition_an(con)   #调用分析条件的函数
show(col,correct)