How to ROLLUP a SUM over multiple columns on separate tables? - mysql

Question

I have 4 tables from which I want to aggregate data using MySQL 5.7.
Projects
+------------+--------+------------------+
| project_id | org_id | name |
+------------+--------+------------------+
| 1 | 1 | Big Project |
| 2 | 1 | Internal Project |
+------------+--------+------------------+
Tasks
+-----------+--------+----------------+------------+
| task_id | org_id | name | project_id |
+-----------+--------+----------------+------------+
| 1 | 1 | Check Work | 1 |
| 2 | 1 | Fix Code | 1 |
| 3 | 1 | Rebuild Office | 2 |
+-----------+--------+----------------+------------+
Resources
+-------------+--------+-------------+-----------+
| resource_id | org_id | first_name | last_name |
+-------------+--------+-------------+-----------+
| 1 | 1 | Alice | Black |
| 2 | 1 | Bob | Smith |
| 3 | 1 | Charlie | White |
+-------------+--------+-------------+-----------+
Task_Details
+-------------+--------+---------+-------------+
| resource_id | org_id | task_id | total_hours |
+-------------+--------+---------+-------------+
| 1 | 1 | 1 | 12 |
| 2 | 1 | 1 | 4 |
| 3 | 1 | 1 | 8 |
| 2 | 1 | 2 | 4 |
| 3 | 1 | 2 | 4 |
| 1 | 1 | 3 | 16 |
+-------------+--------+---------+-------------+
I want to SUM the total_hours, GROUPing by task and project, while still showing the total_hours each employee has individually spent on a task. The output I'm looking for would be something like this
Desired Output
+------------------+----------------+------------+-----------+-------------+
| project_name | task_name | first_name | last_name | total_hours |
+------------------+----------------+------------+-----------+-------------+
| Big Project | Check Work | Alice | Green | 12 |
| Big Project | Check Work | Bob | Smith | 4 |
| Big Project | Check Work | Charlie | Brown | 8 |
| Big Project | Check Work | NULL | NULL | 24 |
| Big Project | Fix Code | Bob | Smith | 4 |
| Big Project | Fix Code | Charlie | Brown | 4 |
| Big Project | Fix Code | NULL | NULL | 8 |
| Big Project | NULL | NULL | NULL | 32 |
| Internal Project | Rebuild Office | Alice | Green | 16 |
| Internal Project | Rebuild Office | NULL | NULL | 16 |
| Internal Project | NULL | NULL | NULL | 16 |
+------------------+----------------+------------+-----------+-------------+
I've managed to create a query that JOINs the relevant tables together, and even managed to GROUP them by project_id, task_id and resource_id. However, adding a WITH ROLLUP statement to the end of my query causes it to fail even though it works without one.
This is my current query:
SELECT
t1.project_name,
t1.task_name,
t2.first_name,
t2.last_name,
SUM(t1.task_hours)
FROM (
SELECT
Projects.project_id,
Projects.name AS project_name,
Tasks.task_id,
Tasks.name AS task_name,
Resources.resource_id,
Task_Details.total_hours AS task_hours
FROM
Projects
RIGHT OUTER JOIN
Tasks
ON
Projects.org_id = Tasks.org_id AND
Projects.project_id = Tasks.project_id
LEFT OUTER JOIN
Task_Details
ON
Task_Details.org_id = Tasks.org_id AND
Task_Details.task_id = Tasks.task_id
LEFT OUTER JOIN
Resources
ON
Resources.org_id = Task_Details.org_id AND
Resources.resource_id = Task_Details.resource_id
WHERE
Projects.org_id = 1
) AS t1
JOIN (
SELECT
resource_id,
first_name,
last_name
FROM
Resources
WHERE
org_id = 1
) AS t2
ON
t2.resource_id = t1.resource_id
GROUP BY
t1.project_id,
t1.task_id,
t1.resource_id;
How can I modify my query such that WITH ROLLUP works?
My SQLFiddle is here, but notably is for MySQL 5.6 rather than 5.7

Answer 1

IMHO, the problem with your query is this: You select some columns which are not in the GROUP BY. That causes some non-sensical values in the columns first_name, last_name, project_name and task_name. However, the sum column is probably correct, isn't it?
This works for me:
SELECT p.name as project_name,
s1.task_name,
first_name,
last_name,
s1.total_hours
FROM (
SELECT
t.project_id,
t.name as task_name,
h.resource_id,
sum(h.total_hours) as total_hours
FROM Task_Details as h
JOIN Tasks as t ON (t.task_id=h.task_id)
GROUP BY t.project_id, t.name, h.resource_id WITH ROLLUP
) AS s1
LEFT JOIN Resources AS r ON (s1.resource_id=r.resource_id)
JOIN Projects AS p ON (p.project_id=s1.project_id);
The nested SELECT does the interesting work, it sums up the total_hours of every resource_id, every task_name and and every project_id. The nesting SELECT then collects the name of every resource and project.
OUTPUT:
+------------------+----------------+------------+-----------+-------------+
| project_name | task_name | first_name | last_name | total_hours |
+------------------+----------------+------------+-----------+-------------+
| Big Project | NULL | NULL | NULL | 32 |
| Big Project | Check Work | Alice | Green | 12 |
| Big Project | Check Work | NULL | NULL | 24 |
| Big Project | Check Work | Bob | Smith | 4 |
| Big Project | Check Work | Charlie | Brown | 8 |
| Big Project | Fix Code | Bob | Smith | 4 |
| Big Project | Fix Code | Charlie | Brown | 4 |
| Big Project | Fix Code | NULL | NULL | 8 |
| Internal Project | NULL | NULL | NULL | 16 |
| Internal Project | Rebuild Office | NULL | NULL | 16 |
| Internal Project | Rebuild Office | Alice | Green | 16 |
+------------------+----------------+------------+-----------+-------------+
Hope this helps.