Using different columns values twice in a single SQL query? - sql

Question

I have a mySQL table called "User" containing multiple mixed values as this:
[user_id] [user_email] [birthday]
---------------------------------
1 x#xxx.com 01/01/1981
2 y#yyy.com 02/02/1982
3 z#zzz.com 03/03/1983
I have another table called "Name" which contains name of the user, but also of some movies like this:
[node_id] [name] [user_id]
----------------------------------
9 John Doe 1
10 Star Wars 90
11 Mike Smith 2
12 Mary Lord 3
13 Rocky III 91
Finally, I have a third table named "Vote" with which is a relationship between a user and some movies he likes.
[vote_id] [node_id] [user_id]
------------------------------
1 10 1
2 10 2
3 13 1
12 10 3
13 13 2
What I'm struggling to do is pull a query with twice the "name" value for two separate things: the name of the user, and the name of the movie he likes. Like this:
[user_id] [user_name] [Birthday] [movie_name]
-------------------------------------------------
1 John Doe 01/01/1981 Star Wars
2 Mike Smith 02/02/1982 Star Wars
1 John Doe 01/01/1981 Rocky III
3 Mary Lord 03/03/1983 Rocky III
2 Mike Smith 02/02/1982 Rocky III
SELECT user.id,
node.name,
user.birthday,
IF(node.type = "movie", node.name, "")
FROM user,
node
JOIN vote ON vote.user_id = user.user_id
WHERE user.id = node.id
I think I'm all mixed up... anyone can help please?

Answer 1

Assuming your schema is exactly what you posted above this should work verbatim.
Query
SELECT user.user_id,
node.name user_name,
user.birthday,
(select node.name from node where node_id = vote.node_id) as movie_name
FROM user
JOIN node ON user.user_id = node.user_id
JOIN vote ON vote.user_id = user.user_id
Result

Answer 2

You have got the database structure wrong. Store the user name in your first table "User"

Answer 3

I would strongly suggest that you store the user_name in the users table. With that change you can then have a much more simple query and a properly normalized schema.
New proposed schema.
users table
(Added user_name column)
[user_id][name][user_email][birthday]
1 name1 x#xxx.com 01/01/1981
2 name2 y#yyy.com 02/02/1982
3 name3 z#zzz.com 03/03/1983
nodes table (call this movies)
(removed user entries and the user_id column as you'll be using votes to link these to users)
[node_id] [name]
10 Star Wars
11 Mike Smith
12 Mary Lord
13 Rocky III
votes table (call this something like movies_users)
(removed the vote_id column as it's just a join table)
[node_id] [user_id]
10 1
10 2
13 1
10 3
13 2
Then your query should look something like this:
select users.user_id, users.name, users.birthday, nodes.name as movie_name
from users
join votes on users.id = votes.user_id
join nodes on votes.node_id = nodes.node_id

Answer 4

select user_id,user_name,birthday,name
from user,name,vote
where (and here you do all the joins like user_id from one table equals user_id from another table)
But here we have a problem which makes me impossible to understand how to write the correct code you have 2 fields in two different tables, user_name and name, you want to join the tables by this name? I don't understand.) I think you are mixing the movie names with the user names, reformulate the question please

Answer 5

I agree with the other answers that you would be better off if you moved the user name into the user table. However, if you are stuck with your current table structure, try this:
SELECT user.id,
uname.name user_name,
user.birthday,
movie.name movie_name
FROM user
JOIN node uname ON uname.user_id = user.user_id
JOIN vote ON vote.user_id = user.user_id
JOIN node movie ON vote.node_id = movie.id
(Assuming votes can only be cast for Movies, it should be unnecessary to blank out non-movies as these should never exist.)