Python Data Access 简明教程

Python MySQL - Order By

在使用 SELECT 查询获取数据时, يمكنك使用 OrderBy 子句以所需的順序(升序或降序)对结果进行排序。默认情况下,此子句按升序对结果进行排序,如果你需要按降序排列结果,则需要明确使用“DESC”。

Syntax

以下是 SELECT column-list 的语法

FROM table_name
[WHERE condition]
[ORDER BY column1, column2,.. columnN] [ASC | DESC]; of the ORDER BY clause:

Example

假设我们在 MySQL 中使用 EMPLOYEES 作为名称创建了一个表格,如下所示:

mysql> CREATE TABLE EMPLOYEE(
   FIRST_NAME CHAR(20) NOT NULL,
   LAST_NAME CHAR(20),
   AGE INT,
   SEX CHAR(1),
   INCOME FLOAT
);
Query OK, 0 rows affected (0.36 sec)

如果使用 INSERT 语句向其中插入了 4 条记录,如下所示:

mysql> INSERT INTO EMPLOYEE VALUES
   ('Krishna', 'Sharma', 19, 'M', 2000),
   ('Raj', 'Kandukuri', 20, 'M', 7000),
   ('Ramya', 'Ramapriya', 25, 'F', 5000),
   ('Mac', 'Mohan', 26, 'M', 2000);

以下语句按升序检索 EMPLOYEE 表的内容。

mysql> SELECT * FROM EMPLOYEE ORDER BY AGE;
+------------+-----------+------+------+--------+
| FIRST_NAME | LAST_NAME | AGE  | SEX  | INCOME |
+------------+-----------+------+------+--------+
| Krishna    | Sharma    |   19 |    M |   2000 |
| Raj        | Kandukuri |   20 |    M |   7000 |
| Ramya      | Ramapriya |   25 |    F |   5000 |
| Mac        | Mohan     |   26 |    M |   2000 |
+------------+-----------+------+------+--------+
4 rows in set (0.04 sec)

你还可以使用 DESC 按降序检索数据,如下所示:

mysql> SELECT * FROM EMPLOYEE ORDER BY FIRST_NAME, INCOME DESC;
+------------+-----------+------+------+--------+
| FIRST_NAME | LAST_NAME | AGE  | SEX  | INCOME |
+------------+-----------+------+------+--------+
| Krishna    | Sharma    |   19 |    M |   2000 |
| Mac        | Mohan     |   26 |    M |   2000 |
| Raj        | Kandukuri |   20 |    M |   7000 |
| Ramya      | Ramapriya |   25 |    F |   5000 |
+------------+-----------+------+------+--------+
4 rows in set (0.00 sec)

ORDER BY clause using python

要按特定顺序检索表的某个内容,调用游标对象上的 execute() 方法,并将 SELECT 语句和 ORDER BY 子句作为参数传递给它。

Example

在以下示例中,我们使用 ORDER BY 子句创建了一个名为 Employee 的表,对其进行填充,然后按其年龄的(升序)顺序检索其记录。

import mysql.connector

#establishing the connection
conn = mysql.connector.connect(
   user='root', password='password', host='127.0.0.1', database='mydb')

#Creating a cursor object using the cursor() method
cursor = conn.cursor()

#Doping EMPLOYEE table if already exists.
cursor.execute("DROP TABLE IF EXISTS EMPLOYEE")
sql = '''CREATE TABLE EMPLOYEE(
   FIRST_NAME CHAR(20) NOT NULL,
   LAST_NAME CHAR(20),
   AGE INT,
   SEX CHAR(1),
   INCOME FLOAT
)'''
cursor.execute(sql)

#Populating the table
insert_stmt = "INSERT INTO EMPLOYEE (FIRST_NAME, LAST_NAME, AGE, SEX, INCOME)
   VALUES (%s, %s, %s, %s, %s)"

data = [('Krishna', 'Sharma', 26, 'M', 2000),
   ('Raj', 'Kandukuri', 20, 'M', 7000),
   ('Ramya', 'Ramapriya', 29, 'F', 5000),
   ('Mac', 'Mohan', 26, 'M', 2000)]
cursor.executemany(insert_stmt, data)
conn.commit()

#Retrieving specific records using the ORDER BY clause
cursor.execute("SELECT * from EMPLOYEE ORDER BY AGE")
print(cursor.fetchall())

#Closing the connection
conn.close()

Output

[('Raj', 'Kandukuri', 20, 'M', 7000.0),
   ('Krishna', 'Sharma', 26, 'M', 2000.0),
   ('Mac', 'Mohan', 26, 'M', 2000.0),
   ('Ramya', 'Ramapriya', 29, 'F', 5000.0)
]

同样,你可以使用 ORDER BY 子句按降序从表中检索数据。

Example

import mysql.connector

#establishing the connection
conn = mysql.connector.connect(
   user='root', password='password', host='127.0.0.1', database='mydb')

#Creating a cursor object using the cursor() method
cursor = conn.cursor()

#Retrieving specific records using the ORDERBY clause
cursor.execute("SELECT * from EMPLOYEE ORDER BY INCOME DESC")
print(cursor.fetchall())

#Closing the connection
conn.close()

Output

[('Raj', 'Kandukuri', 20, 'M', 7000.0),
   ('Ramya', 'Ramapriya', 29, 'F', 5000.0),
   ('Krishna', 'Sharma', 26, 'M', 2000.0),
   ('Mac', 'Mohan', 26, 'M', 2000.0)
]