Python Sqlite 简明教程
Python SQLite - Order By
使用 SELECT 查询获取数据时，您将按照插入记录的顺序获取记录。
您可以使用 Order By 子句按所需顺序（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。如果您需要按降序对结果进行排序，您需要显式使用 “DESC”。
Syntax
以下是 SQLite 中 ORDER BY 子句的语法。
SELECT column-list
FROM table_name
[WHERE condition]
[ORDER BY column1, column2, .. columnN] [ASC | DESC];Example
假设我们使用以下查询创建了一个名为 CRICKETERS 的表 -
sqlite> CREATE TABLE CRICKETERS (
First_Name VARCHAR(255),
Last_Name VARCHAR(255),
Age int,
Place_Of_Birth VARCHAR(255),
Country VARCHAR(255)
);
sqlite>并且如果我们使用 INSERT 语句向其中插入 5 条记录，如下所示 -
sqlite> insert into CRICKETERS values('Shikhar', 'Dhawan', 33, 'Delhi', 'India');
sqlite> insert into CRICKETERS values('Jonathan', 'Trott', 38, 'CapeTown', 'SouthAfrica');
sqlite> insert into CRICKETERS values('Kumara', 'Sangakkara', 41, 'Matale', 'Srilanka');
sqlite> insert into CRICKETERS values('Virat', 'Kohli', 30, 'Delhi', 'India');
sqlite> insert into CRICKETERS values('Rohit', 'Sharma', 32, 'Nagpur', 'India');
sqlite>选择语句检索 CRICKETERS 表的行按升序排列它们的年龄—
sqlite> SELECT * FROM CRICKETERS ORDER BY AGE;
First_Name Last_Name Age Place_Of_B Country
---------- ---------- ---- ---------- -----------
Virat Kohli 30 Delhi India
Rohit Sharma 32 Nagpur India
Shikhar Dhawan 33 Delhi India
Jonathan Trott 38 CapeTown SouthAfrica
Kumara Sangakkara 41 Matale Srilanka
sqlite>您可以使用多个列对表的记录进行排序。以下 SELECT 语句基于列 AGE 和 FIRST_NAME 对 CRICKETERS 表的记录进行排序。
sqlite> SELECT * FROM CRICKETERS ORDER BY AGE, FIRST_NAME;
First_Name Last_Name Age Place_Of_B Country
---------- ---------- ---- ---------- -------------
Virat Kohli 30 Delhi India
Rohit Sharma 32 Nagpur India
Shikhar Dhawan 33 Delhi India
Jonathan Trott 38 CapeTown SouthAfrica
Kumara Sangakkara 41 Matale Srilanka
sqlite>默认情况下， ORDER BY 子句按升序对表的记录进行排序。您可以使用 DESC 按降序排列结果，如下所示：
sqlite> SELECT * FROM CRICKETERS ORDER BY AGE DESC;
First_Name Last_Name Age Place_Of_B Country
---------- ---------- ---- ---------- -------------
Kumara Sangakkara 41 Matale Srilanka
Jonathan Trott 38 CapeTown SouthAfrica
Shikhar Dhawan 33 Delhi India
Rohit Sharma 32 Nagpur India
Virat Kohli 30 Delhi India
sqlite>ORDER BY Clause Using Python
要以特定顺序检索表的全表，请对光标对象调用 execute() 方法，并将 SELECT 语句连同 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 psycopg2
#establishing the connection
conn = psycopg2.connect(
database="mydb", user='postgres', password='password', host='127.0.0.1', port= '5432'
)
#Setting auto commit false
conn.autocommit = True
#Creating a cursor object using the cursor() method
cursor = conn.cursor()
#Doping EMPLOYEE table if already exists.
cursor.execute("DROP TABLE IF EXISTS EMPLOYEE")
#Creating a table
sql = '''CREATE TABLE EMPLOYEE(
FIRST_NAME CHAR(20) NOT NULL,
LAST_NAME CHAR(20),
AGE INT, SEX CHAR(1),
INCOME INT,
CONTACT INT
)'''
cursor.execute(sql)
#Populating the table
#Populating the table
cursor.execute(
'''INSERT INTO EMPLOYEE(FIRST_NAME, LAST_NAME, AGE, SEX, INCOME)
VALUES ('Ramya', 'Rama priya', 27, 'F', 9000),
('Vinay', 'Battacharya', 20, 'M', 6000),
('Sharukh', 'Sheik', 25, 'M', 8300),
('Sarmista', 'Sharma', 26, 'F', 10000),
('Tripthi', 'Mishra', 24, 'F', 6000)''')
conn.commit()
#Retrieving specific records using the ORDER BY clause
cursor.execute("SELECT * from EMPLOYEE ORDER BY AGE")
print(cursor.fetchall())
#Commit your changes in the database
conn.commit()
#Closing the connection
conn.close()