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📜  Python SQLite-加入

📅  最后修改于: 2020-11-06 05:59:03             🧑  作者: Mango

将数据分为两个表后，可以使用Joins从这两个表中获取组合记录。

例

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>

让我们再创建一个表OdiStats，用于描述CRICKETERS表中每个球员的一日板球统计数据。

sqlite> CREATE TABLE ODIStats (
   First_Name VARCHAR(255),
   Matches INT,
   Runs INT,
   AVG FLOAT,
   Centuries INT,
   HalfCenturies INT
);
sqlite>

以下语句检索结合这两个表中的值的数据-

sqlite> SELECT
   Cricketers.First_Name, Cricketers.Last_Name, Cricketers.Country,
   OdiStats.matches, OdiStats.runs, OdiStats.centuries, OdiStats.halfcenturies
   from Cricketers INNER JOIN OdiStats ON Cricketers.First_Name = OdiStats.First_Name;
First_Name  Last_Name   Country  Matches  Runs   Centuries   HalfCenturies
----------  ----------  -------  -------  ----   ---------   -------------- 
Shikhar     Dhawan      Indi     133      5518   17          27
Jonathan    Trott       Sout     68       2819   4           22
Kumara      Sangakkara  Sril     404      14234  25          93
Virat       Kohli       Indi     239      11520  43          54
Rohit       Sharma      Indi     218      8686   24          42
sqlite>

使用Python加入子句

以下SQLite示例，使用Python演示了JOIN子句-

import sqlite3
#Connecting to sqlite
conn = sqlite3.connect('example.db')

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

#Retrieving data
sql = '''SELECT * from EMP INNER JOIN CONTACT ON EMP.CONTACT = CONTACT.ID'''

#Executing the query
cursor.execute(sql)

#Fetching 1st row from the table
result = cursor.fetchall();

print(result)

#Commit your changes in the database
conn.commit()

#Closing the connection
conn.close()

输出

[
   ('Ramya', 'Rama priya', 27, 'F', 9000.0, 101, 101, 'Krishna@mymail.com', 'Hyderabad'), 
   ('Vinay', 'Battacharya', 20, 'M', 6000.0, 102, 102,'Raja@mymail.com', 'Vishakhapatnam'), 
   ('Sharukh', 'Sheik', 25, 'M', 8300.0, 103, 103, 'Krishna@mymail.com', 'Pune'), 
   ('Sarmista', 'Sharma', 26, 'F', 10000.0, 104, 104, 'Raja@mymail.com', 'Mumbai')
]