数据存储之关系型数据库存储---MySQL存储

MySQL的存储

• 利用PyMySQL连接MySQL

  • 连接数据库

    import pymysql
    
    # 连接MySQL           MySQL在本地运行      用户名为root         密码为123456    默认端口3306
    db = pymysql.connect(host='localhost', user='root', password='', port=3306)
    
    # cursor()方法获得MySQL的操作游标，利用游标来执行SQL语句，其中执行方法为execute()
    cursor = db.cursor()
    
    # 获取MySQL的当前版本
    cursor.execute('SELECT VERSION()')
    
    # fetchone()方法获得第一条数据，即版本号
    data = cursor.fetchone()
    print('Database version:', data)
    
    # 创建一个名为reptile的数据库,默认编码为utf8mb4
    cursor.execute("CREATE DATABASE reptile DEFAULT CHARACTER SET utf8mb4")
    db.close()
    
    # 运行输出：
    Database version: ('8.0.16',)
    # 运行生成一个名为reptile的数据库

  • 创建表

    import pymysql
    
    db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
    cursor = db.cursor()
    sql = '''CREATE TABLE
          IF NOT EXISTS students
          (
          id VARCHAR(255) NOT NULL,
          name VARCHAR(255) NOT NULL,
          age INT NOT NULL,
          PRIMARY KEY (id)
          )'''
    # 创建一个名为students的数据表，主键为id
    cursor.execute(sql)
    db.close()
    
    # 运行创建一个数据表

  • 插入数据

    import pymysql
    
    id = ''
    user = 'Lee Hua'
    age = 20
    
    # 连接数据库
    db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
    # 获得MySQL的操作游标
    cursor = db.cursor()
    sql = '''INSERT INTO students(id, name, age) VALUES(%s %s %s)'''
    
    try:
        # 执行
        cursor.execute(sql, (id, user, age))
        # 数据插入、更新、删除操作，都需要用到commit()方法才能生效
        db.commit()
    
    except:
        # 调用rollback()执行数据回滚，相当于什么都没有发生过
        db.rollback()
    
    db.close()
    
    # 运行，数据被插入到数据表中

    import pymysql
    
    db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
    cursor = db.cursor()
    
    data = {
        'id': '',
        'user': 'Lao wang',
        'age': 19
    }
    table_name = 'students'
    keys = ', '.join(data.keys())                   # id, user, age
    values = ', '.join(['%s'] * len(data))          # ['%s', '%s', ......]   len(data)个'%s'
    sql = '''INSERT INTO {table_name}({keys}) VALUES({values})'''.format(table_name=table_name, keys=keys, values=values)
    # sql = INSERT INTO students(id, name, age) VALUES(%s %s %s)
    
    try:
        tuple_ = tuple(data.values())
        if cursor.execute(sql, tuple_):
            print('成功插入数据')
        db.commit()
    
    except:
        print('插入数据失败')
        db.rollback()
    
    db.close()
    
    # 与上面一个例子做比较

  • 更新数据

    import pymysql
    
    db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
    cursor = db.cursor()
    
    sql = 'UPDATA students SET age = %s WHERE name = %s'
    try:
        cursor.execute(sql, (25, 'Bob'))
        db.commit()
    except:
        db.rollback()
    
    db.close()
    
    简单方式数据更新

    简单方式数据更新

    # 实现去重（如果数据存在，则更新数据；如果数据不存在，则插入数据。）

    import pymysql
    
    db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
    cursor = db.cursor()
    
    data = {
        'id': '',
        'user': 'Lao wang',
        'age': 19
    }
    table_name = 'students'
    keys = ', '.join(data.keys())                               # keys = id, name, age
    values = ', '.join(['%s'] * len(data))                      # values = %s, %s, %s
    update = ', '.join(
        [" {key} = %s".format(key=key) for key in data]
    )                                                           # id = %s, name = %s, age = %s
    sql = '''INSERT INTO {table_name}({keys}) VALUES({values}) ON DUPLICATE KEY update'''.format(table_name=table_name, keys=keys, values=values)
    # ON DUPLICATE KEY UPDATE 表示：如果主键已经存在，那么就执行更新操作
    
    try:
        tuple_ = tuple(data.values())
        if cursor.execute(sql, tuple_):
            print('成功插入数据')
        db.commit()
    
    except:
        print('插入数据失败')
        db.rollback()
    
    db.close()

  • 删除数据

    import pymysql
    
    db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
    cursor = db.cursor()
    
    table = 'students'
    condition = 'age > 20'
    sql = 'DELETE FROM {table} WHERE {conditon}'.format(table=table, conditon=condition)
    try:
        cursor.execute(sql)
        db.commit()
    except:
        db.rollback()
    
    db.close()
    
    # 删除age > 20的数据

    简单示例

  • 查询数据

    import pymysql
    
    db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
    cursor = db.cursor()
    
    sql = 'SELECT * FROM students WHERE age >= 20'
    try:
        cursor.execute(sql)
        print('Count:', cursor.rowcount)        # 调用cursor的rowcount属性，获取查询结果的条数
        one = cursor.fetchone()                 # 获取结果的第一条信息
        print('One:', one)
        result = cursor.fetchall()              # 获取结果的所有数据
        print('Result:', result)
        print('Result Type:', type(result))
        for row in result:
            print(row)
    except:
        print('Error')
    
    # 输出：
    Count: 0
    One: None
    Result: ()
    Result Type: <class 'tuple'>

    一次性查询所有数据----fetchall()

    import pymysql
    
    db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
    cursor = db.cursor()
    
    sql = 'SELECT * FROM students WHERE age >= 20'
    try:
        cursor.execute(sql)
        print('Count:', cursor.rowcount)        # 调用cursor的rowcount属性，获取查询结果的条数
        row = cursor.fetchone()                 # 获取结果的第一条数据
        while row:
            print('Row:', row)
            row = cursor.fetchone()
    except:
        print('Error')

    逐条查询数据----fatchone()