Python和SQLite3从两个表中选择

Question

I have written this code in python, which I basically opens up my SQLite3 database and looks at each row in the table 'contact' and then takes each 'id' number and then looks at the matching 'id' in the table 'Users'. My problem is that it only outputs the first one and does not loop through all the rows.

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()

Any suggestions, I'm very new to python.

Answer 1

You can ask the database to do a join instead:

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)

The INNER JOIN tells SQLite to only pick rows for which there is an actual match on the id columns. If you marked the id column as a foreign key in the contact table, you could use a NATURAL INNER JOIN as well, and omit the ON clause.

Answer 2

If I understand you:

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)