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📜  Python SQLite-加入

📅  最后修改于: 2020-11-07 08:58:57             🧑  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的Join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')]