Python和SQLite3从两个表中选择

Question

我已经用python编写了这段代码，基本上我打开了SQLite3数据库，查看了表“ contact”中的每一行，然后获取了每个“ id”号，然后查看了“ Users”表中的匹配“ id” 。 我的问题是，它仅输出第一个，而不循环遍历所有行。

import sqlite3

conn = sqlite3.connect('sqlite3.db')

cursor = conn.cursor()
cursor2 = conn.cursor()
cursor3 = conn.cursor()

text_file = open("Output.txt", "w");
try:
    cursor.execute("SELECT Id, address FROM contact;") # Get address details by ID
    for row in cursor:
        ID = row[0]
        address= row[1]

        cursor2.execute("SELECT name FROM Users WHERE id= " + str(ID) + ";") # Get users's name by ID
        row2 = cursor2.fetchone()
        sendername = row2[0]

        text_file.write(firstname, lastname, address);


finally:
    conn.close()

任何建议，我对python都是新手。

Answer 1

您可以要求数据库进行联接：

cursor.execute("""\
    SELECT u.name, c.address
    FROM contact c
    INNER JOIN Users u ON u.id = c.Id
    """)
with open('Output.txt', 'w') as outfh:
    for name, address in cursor:
        outfh.write('{} {}\n'.format(name, address)

INNER JOIN告诉SQLite只选择id列上实际匹配的行。 如果在contact表中将id列标记为外键，则也可以使用NATURAL INNER JOIN ，并省略ON子句。

Answer 2

如果我了解您：

cursor.execute("SELECT Users.name, contact.address FROM Users, contact WHERE contact.Id = Users.id;")
for row in cursor:
    name= row[0]
    address= row[1]
    text_file.write(name+" "+address)