MYSQL Query - Some results don't return - mysql

Question

I have a problem im my sql query:
SELECT table_2.id, SUM(table_2.time + table_4.time + table_6.time + table_8.time + table_10.time + table_12.time) AS total_time, SUM(table_2.connects + table_4.connects + table_6.connects + table_8.connects + table_10.connects + table_12.connects) AS total_connects FROM table_2
INNER JOIN table_4 ON table_2.id = table_4.id
INNER JOIN table_6 ON table_2.id = table_6.id
INNER JOIN table_8 ON table_2.id = table_8.id
INNER JOIN table_10 ON table_2.id = table_10.id
INNER JOIN table_12 ON table_2.id = table_12.id
GROUP BY table_2.authid ORDER BY total_time DESC
Ok, I have a script that grabs the user IDS and the time they spent and then puts it in mysql tables depending on which forum they have entered. The query above seems to be working fine but only for the users that have entered all forums, because the others that haven't entered in all forums don't return any result.
The ID is always the same, it is the users ID and connects is the number of times the user enters the specific forum.
If you understand my problem and know the answear please let me know, otherwise I'll try to explain better
Thanks

Answer 1

I think a good way to do this may be:
SELECT id, SUM(time), SUM(connects)
FROM (
SELECT id, time, connects FROM table_2
UNION ALL
SELECT id, time, connects FROM table_4
UNION ALL
SELECT id, time, connects FROM table_6
UNION ALL
SELECT id, time, connects FROM table_8
UNION ALL
SELECT id, time, connects FROM table_10
UNION ALL
SELECT id, time, connects FROM table_12
) uniontable
GROUP BY id
Since they all have the same fields.
EDIT: And it sounds like it may not be such a strange idea to merge them into one table, especially if you want to count the total time like this ;)
EDIT 2: I'm sorry, that wasn't valid SQL at all. This should be better.

Answer 2

Replace the INNER JOIN by a LEFT OUTER JOIN this will get you results over all the tables. You might need to re-define the SUM probably you'll get NULL on users who haven't visited all forums...

Answer 3

Replace the JOIN with the LEFT JOIN:
SELECT people.id, SUM(COALESCE(table_2.time, 0) + COALESCE(table_4.time, 0) + table_6.time, 0) + COALESCE(table_8.time, 0) + COALESCE(table_10.time, 0) + COALESCE(table_12.time, 0)) AS total_time,
SUM(COALESCE(table_2.connects, 0) + COALESCE(table_4.connects, 0) + COALESCE(table_6.connects, 0) + COALESCE(table_8.connects, 0) + COALESCE(table_10.connects, 0) + COALESCE(table_12.connects, 0)) AS total_connects
FROM people p
LEFT JOIN
table_2
ON table_2.id = people.id
LEFT JOIN
table_4
ON people.id = table_4.id
LEFT JOIN
table_6
ON people.id = table_6.id
LEFT JOIN
table_8
ON people.id = table_8.id
LEFT JOIN
table_10
ON people.id = table_10.id
LEFT JOIN
table_12
ON people.id = table_12.id
GROUP BY
people.authid
ORDER BY
total_time DESC

Answer 4

#afonso: I think you should populate all those time tables whenever a new user is created by inserting the user with a time of 0 (just so that they're in the table). Would this be an acceptable compromise for your application just to have those users in the tables so your initial query will work?

Answer 5

You will need to use outer joins and you will need to use IFNULL or something similar to map the "user wasn't in forum" nulls to zeroes.
SELECT t2.id,
SUM(IFNULL(t2.time, 0) + IFNULL(t4.time, 0) +
IFNULL(t6.time, 0) + IFNULL(t8.time, 0) +
IFNULL(t10.time, 0) + IFNULL(t12.time, 0)) AS total_time,
SUM(IFNULL(t2.connects, 0) + IFNULL(t4.connects, 0) +
IFNULL(t6.connects, 0) + IFNULL(t8.connects, 0) +
IFNULL(t10.connects, 0) + IFNULL(t12.connects, 0)) AS total_connects
FROM table_2 AS t2
LEFT JOIN table_4 AS t4 ON t2.id = t4.id
LEFT JOIN table_6 AS 76 ON t2.id = t6.id
LEFT JOIN table_8 AS t8 ON t2.id = t8.id
LEFT JOIN table_10 AS t10 ON t2.id = t10.id
LEFT JOIN table_12 AS t12 ON t2.id = t12.id
GROUP BY t2.id ORDER BY total_time DESC
This almost works; it does work for all users that visit the forum for which the information is stored in table_2. To make it work for people who don't visit the 'table_2 forum', the query needs to use the table that defines users and do the outer joins with that table:
SELECT u.id,
SUM(IFNULL(t2.time, 0) + IFNULL(t4.time, 0) +
IFNULL(t6.time, 0) + IFNULL(t8.time, 0) +
IFNULL(t10.time, 0) + IFNULL(t12.time, 0)) AS total_time,
SUM(IFNULL(t2.connects, 0) + IFNULL(t4.connects, 0) +
IFNULL(t6.connects, 0) + IFNULL(t8.connects, 0) +
IFNULL(t10.connects, 0) + IFNULL(t12.connects, 0)) AS total_connects
FROM Users AS u
LEFT JOIN table_2 AS t2 ON u.id = t2.id
LEFT JOIN table_4 AS t4 ON u.id = t4.id
LEFT JOIN table_6 AS 76 ON u.id = t6.id
LEFT JOIN table_8 AS t8 ON u.id = t8.id
LEFT JOIN table_10 AS t10 ON u.id = t10.id
LEFT JOIN table_12 AS t12 ON u.id = t12.id
GROUP BY u.id ORDER BY total_time DESC
However, given the symmetry of the table_N tables, I think you should do as Spiny Norman
suggests and redesign your schema so that there is one table that stores the timing and connection values:
CREATE TABLE ForumUsage
(
ForumID INTEGER NOT NULL REFERENCES Forums,
UserID INTEGER NOT NULL REFERENCES Users,
Time INTEGER NOT NULL,
Connects INTEGER NOT NULL
);
Then you sum over the entries in that table.