database: json format and sqlite

[izan]

Hi!
I have to do the following task:
The application will read roster data in JSON format, parse the file, and then produce an SQLite database that contains a User, Course, and Member table and populate the tables from the data file.

You can base your solution on this code: http://www.py4e.com/code3/roster/roster.py - this code is incomplete as you need to modify the program to store the role column in the Member table to complete the assignment.

My programme:

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import json import sqlite3   conn = sqlite3.connect('rosterdb.sqlite') cur = conn.cursor()   # Do some setup cur.executescript(''' DROP TABLE IF EXISTS User; DROP TABLE IF EXISTS Member; DROP TABLE IF EXISTS Course;     CREATE TABLE User (     id     INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,     name   TEXT UNIQUE );   CREATE TABLE Course (     id     INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,     title  TEXT UNIQUE );   CREATE TABLE Member (     user_id     INTEGER,     course_id   INTEGER,     role        INTEGER,     PRIMARY KEY (user_id, course_id) ) ''')   fname = input('Enter file name: ') if len(fname) < 1:     fname = 'roster_data.json'   # [ #   [ "Charley", "si110", 1 ], #   [ "Mea", "si110", 0 ],   str_data = open(fname).read() json_data = json.loads(str_data)   for entry in json_data:       name = entry[0]     title = entry[1]     role= entry[2]       print((name, title, role))       cur.execute('''INSERT OR IGNORE INTO User (name)         VALUES ( ? )''', ( name, ) )     cur.execute('SELECT id FROM User WHERE name = ? ', (name, ))     user_id = cur.fetchone()[0]       cur.execute('''INSERT OR IGNORE INTO Course (title)         VALUES ( ? )''', ( title, ) )     cur.execute('SELECT id FROM Course WHERE title = ? ', (title, ))     course_id = cur.fetchone()[0]       cur.execute('''INSERT OR IGNORE INTO Member (role)         VALUES ( ? )''', ( role, ) )                   cur.execute('''INSERT OR REPLACE INTO Member         (user_id, course_id) VALUES ( ?, ?)''',         ( user_id, course_id ) )       conn.commit()

The the task says:
Once you have made the necessary changes to the program and it has been run successfully reading the above JSON data, run the following SQL command:

Output:
SELECT User.name,Course.title, Member.role FROM 
    User JOIN Member JOIN Course 
    ON User.id = Member.user_id AND Member.course_id = Course.id
    ORDER BY User.name DESC, Course.title DESC, Member.role DESC LIMIT 2;

The output should look as follows:

Output:
Zuriel|si430|0
Zofia|si363|0

With my programme I get the following (I suppose it is what I have to obtain):

Output:
('Mehraz', 'si310', 0)
('Tobie', 'si310', 0)
('Naila', 'si310', 0)
('Asif', 'si310', 0)
('Derren', 'si310', 0)
('Abdulkadir', 'si310', 0)

The problem comes here:
Then the task says: Once that query gives the correct data, run this query:

Output:
SELECT 'XYZZY' || hex(User.name || Course.title || Member.role ) AS X FROM 
    User JOIN Member JOIN Course 
    ON User.id = Member.user_id AND Member.course_id = Course.id
    ORDER BY X LIMIT 1;

You should get one row with a string that looks like XYZZY53656C696E613333.

I think there is something wrong with this query because it does not work. Any ideas? Thank you in advance

buran write Dec-28-2021, 03:19 PM:
Please, use proper tags when post code, traceback, output, etc. This time I have added tags for you.
See BBcode help for more info.

[ibreeden]

With my programme I get the following (I suppose it is what I have to obtain):

Output:
('Mehraz', 'si310', 0)('Tobie', 'si310', 0)
('Naila', 'si310', 0)
('Asif', 'si310', 0)
('Derren', 'si310', 0)
('Abdulkadir', 'si310', 0)

I can't believe you get this result by executing:

Output:
SELECT User.name,Course.title, Member.role FROM 
    User JOIN Member JOIN Course 
    ON User.id = Member.user_id AND Member.course_id = Course.id
    ORDER BY User.name DESC, Course.title DESC, Member.role DESC LIMIT 2;

It says: "LIMIT 2" but you get 6 records. It also says "ORDER BY User.name DESC" but your names appear in random order.
Please have a sharp look at how you execute this query.