Python MySQL 排序方式
在使用 SELECT 查询获取数据时,你可以使用 OrderBy 子句按所需顺序(升序或降序)对结果进行排序。默认情况下,该子句按升序对结果进行排序,如果需要按降序排列,则需要显式使用“DESC”。
语法
以下是语法 SELECT column-list
FROM table_name [WHERE condition] [ORDER BY column1, column2,.. columnN] [ASC | DESC]; of the ORDER BY clause:
例子
假设我们在 MySQL 中创建了一个名为 EMPLOYEES 的表:
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)
如果我们使用 INSERT 语句向其中插入了 4 条记录:
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);
以下语句按年龄升序检索 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 以降序检索数据,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)
使用 python 的 ORDER BY 子句
要按特定顺序检索表的内容,请调用 执行() 游标对象上的方法,并将 SELECT 语句与 ORDER BY 子句一起作为参数传递给它。
例子
在下面的示例中,我们将使用 ORDER BY 子句创建一个具有名称和 Employee 的表,填充它,并按其年龄的(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()
[('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。
例子
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()
[('Raj', 'Kandukuri', 20, 'M', 7000.0), ('Ramya', 'Ramapriya', 29, 'F', 5000.0), ('Krishna', 'Sharma', 26, 'M', 2000.0), ('Mac', 'Mohan', 26, 'M', 2000.0) ]