python：mysql之ORDER BY 语句

Posted 2021-06-10 就用python

接下来。装逼开始....

ORDER BY 语句用于对结果集进行排序操作

• ORDER BY 语句可以指定任何字段作为排序条件

• ORDER BY 语句也可以指定多个字段作为排序条件

• ORDER BY 语句也可以指定ASC或DESC关键字设置结果集是升序还是降序

• ORDER BY 语句是跟在SQL语句最后面的

• ORDER BY 语句默认情况下是升序排序，也就是执行ASC

示例1：终端执行SQL语句，查询到结果集后并默认排序为升序

mysql> select * from test_user_copy;+----+--------+-------------+----------+-----------+---------------------+| id | name | mobile | address | country | school |+----+--------+-------------+----------+-----------+---------------------+| 1 | JAVA | 18847474541 | Beijing | China | Beijing University || 2 | Python | 17748484242 | Nanjing | Singapore | Nanjing University || 3 | SQL | 17748484246 | Beijing | China | Beijing University || 4 | R | 17748484141 | Shanghai | Singapore | Shanghai University |+----+--------+-------------+----------+-----------+---------------------+4 rows in set (0.00 sec)
mysql> select * from test_user_copy order by country;+----+--------+-------------+----------+-----------+---------------------+| id | name | mobile | address | country | school |+----+--------+-------------+----------+-----------+---------------------+| 1 | JAVA | 18847474541 | Beijing | China | Beijing University || 3 | SQL | 17748484246 | Beijing | China | Beijing University || 2 | Python | 17748484242 | Nanjing | Singapore | Nanjing University || 4 | R | 17748484141 | Shanghai | Singapore | Shanghai University |+----+--------+-------------+----------+-----------+---------------------+4 rows in set (0.00 sec)

示例2：python执行SQL语句，查询到结果集后并设置排序为降序

import pymysql

class MysqlData: def __init__(self, host="localhost", user="root", password="123456", database="testing", port=3306): # 连接数据库 self.connection = pymysql.connect(host=host, user=user, password=password, database=database, port=port, charset='utf8', cursorclass=pymysql.cursors.DictCursor)
 def modify_data(self, sql, args=None): """ Args: sql: sql语句            args:   接收格式化参数 Returns: """ try: with self.connection: self.connection.ping(reconnect=True) with self.connection.cursor() as cursor: # 执行sql语句 cursor.execute(sql, args=args) # 提交sql语句 self.connection.commit() except pymysql.err.MySQLError as _error: raise _error
 def get_data(self, sql, args=None, is_data=False): """ Args: sql: sql语句 args: 接收格式化参数            is_data:    判断获取多条数据还是单个数据，默认获取单个数据 Returns: """ try: with self.connection: self.connection.ping(reconnect=True) with self.connection.cursor() as cursor: # 执行sql语句 cursor.execute(sql, args=args)
 # 返回查询出的数据信息 return cursor.fetchall() if is_data else cursor.fetchone()
 except pymysql.err.MySQLError as _error: raise _error

if __name__ == '__main__': # 初始化类，创建对象 info = MysqlData()
 # 调用查询多条数据方法 results = info.get_data(""" SELECT * FROM test_user_copy ORDER BY country DESC """, is_data=True)  # 循环列表，获取数据 for i in results: print(i)

{'id': 2, 'name': 'Python', 'mobile': '17748484242', 'address': 'Nanjing', 'country': 'Singapore', 'school': 'Nanjing University'}{'id': 4, 'name': 'R', 'mobile': '17748484141', 'address': 'Shanghai', 'country': 'Singapore', 'school': 'Shanghai University'}{'id': 5, 'name': 'C++', 'mobile': '17748484141', 'address': 'Shenzhen', 'country': 'France', 'school': 'Shanghai University'}{'id': 1, 'name': 'JAVA', 'mobile': '18847474541', 'address': 'Beijing', 'country': 'China', 'school': 'Beijing University'}{'id': 3, 'name': 'SQL', 'mobile': '17748484246', 'address': 'Beijing', 'country': 'China', 'school': 'Beijing University'}
Process finished with exit code 0

从返回的结果集可以看到，country这一列已经做了降序排序...

示例3：python执行SQL语句，查询到结果集后并设置id升序、country为降序

if __name__ == '__main__': # 初始化类，创建对象 info = MysqlData()
 # 调用查询多条数据方法 results = info.get_data(""" SELECT * FROM test_user_copy ORDER BY id DESC, country DESC """, is_data=True)  # 循环列表，获取数据  for i in results:        print(i)

{'id': 5, 'name': 'C++', 'mobile': '17748484141', 'address': 'Shenzhen', 'country': 'France', 'school': 'Shanghai University'}{'id': 4, 'name': 'R', 'mobile': '17748484141', 'address': 'Shanghai', 'country': 'Singapore', 'school': 'Shanghai University'}{'id': 3, 'name': 'SQL', 'mobile': '17748484246', 'address': 'Beijing', 'country': 'China', 'school': 'Beijing University'}{'id': 2, 'name': 'Python', 'mobile': '17748484242', 'address': 'Nanjing', 'country': 'Singapore', 'school': 'Nanjing University'}{'id': 1, 'name': 'JAVA', 'mobile': '18847474541', 'address': 'Beijing', 'country': 'China', 'school': 'Beijing University'}
Process finished with exit code 0

从返回的结果集可以看到，优先生效的是id排序...

至此，mysql中使用 ORDER BY 语句查询数据完成...

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