Using an OR clause in my INNER JOIN - mysql

Question

I have the following two tables,
CREATE TABLE logins (
id MEDIUMINT NOT NULL AUTO_INCREMENT,
user_id_1 INT NOT NULL,
user_id_2 INT DEFAULT 0,
user_id_3 INT DEFAULT 0,
PRIMARY KEY (id)
) ENGINE=MyISAM;
CREATE TABLE user_data (
user_id NOT NULL,
day DATE NOT NULL,
PRIMARY KEY (`user_id, `day`)
) ENGINE=MyISAM;
This schema could use a refactor, but I've inherited it and have to write a query now that does a JOIN with both logins and user_data. I need to select all the rows in user_data that have a > 0 value for one of the three user_id_? keys.
I'm not entirely sure how to compile this query, was thinking something along the lines of:
SELECT logins.user_id_1, logins.user_id_2, logins.user_id_3, user_data.day,
FROM logins
INNER JOIN user_data
ON (logins.user_id_1 = user_data.user_id OR ??)
What's the best way to query for this where I will retrieve up to 3 rows, one for each user_id_?

Answer 1

OR is allowed. Another option is to left join to the user_data table three times, and check to see if any of them came back. You might want to try both and see which performs better. My guess is they will be about the same, but I'm not deeply familiar with the MySQL plan generator.
SELECT
l.user_id_1
,l.user_id_2
,l.user_id_3
--consider: what if there is a match in more
--than one table? what do you want to happen?
,case when ud1.day is not null then ud1.day
when ud2.day is not null then ud2.day
when ud3.day is not null then ud3.day
else null
end as day
FROM
logins l
left JOIN user_data ud1 on ud1.user_id = l.user_id_1
left join user_data ud2 on ud2.user_id = l.user_id_2
left join user_data ud3 on ud3.user_id = l.user_id_3
where ud1.user_id is not null
or ud2.user_id is not null
or ud3.user_id is not null

Answer 2

you can use or.
SELECT logins.user_id_1, logins.user_id_2, logins.user_id_3, user_data.day,
FROM logins
INNER JOIN user_data
ON logins.user_id_1 = user_data.user_id OR
logins.user_id_2 = user_data.user_id OR
logins.user_id_3 = user_data.user_id
This syntax will work to choose all the records that match one or the other conditions.

Answer 3

You could try this:
SELECT logins.user_id_1, logins.user_id_2, logins.user_id_3, user_data.day,
FROM logins,user_data
WHERE user_data.user_id in (logins.user_id_1,logins.user_id_2,logins.user_id_3)

Answer 4

You can set any combinations of different conditions when do ON absolutely no limits for OR AND and other boolean operations same as for WHERE clause
SELECT logins.user_id_1, logins.user_id_2, logins.user_id_3, user_data.day,
FROM logins
INNER JOIN user_data
ON logins.user_id_1 = user_data.user_id OR
logins.user_id_2 = user_data.user_id OR
logins.user_id_3 = user_data.user_id
or probably you don't need those logins.user_id_1, logins.user_id_2, logins.user_id_3, but just user_data.user_id:
SELECT user_data.user_id, user_data.day,
FROM logins
INNER JOIN user_data
ON logins.user_id_1 = user_data.user_id OR
logins.user_id_2 = user_data.user_id OR
logins.user_id_3 = user_data.user_id

Answer 5

You might utilize a UNION, this will return multiple rows per login-row, don't know if you need this:
SELECT l.user_id, user_data.*
FROM user_data as u
INNER JOIN
(
select user_id_1 --, could add other columns...
from logins
union
select user_id_2 --, could add other columns...
from logins
where user_id_2 > 0
union
select user_id_3 --, could add other columns...
from logins
where user_id_3 > 0
) as l
ON l.user_id = user_data.user_id