MySQL grouping when using a sub query - mysql

Question

I am trying to create a summary output to show a totals based on values in sub queries and then group the output by a label
Query looks like:
select c.name,
(select sum(duration) from dates d
inner join time t1 on d.time_id=t1.id
where d.employee=t.employee
and d.date >= now() - INTERVAL 12 MONTH) as ad,
(select sum(cost) from dates d
inner join time t1 on d.time_id=t1.id
where d.employee=t.employee
and d.date >= now() - INTERVAL 12 MONTH) as ac
FROM time t
inner join employees ee on t.employee=ee.employee
inner join centres c on ee.centre=c.id
where
ee.centre in (4792,4804,4834) group by c.centre
I want this to show me the ad and ac for each centre but instead it only shows values for ac for the last centre in the list and the rest show as zero
If I remove the group by then I get a list of all the entries but then it is not summarised in any way and I need that rollup view

Answer 1

A SQL statement that is returning a result that is unexpected is not a whole lot to go on.
Without a specification, helpfully illustrated with sample data and expected output, we're just guessing at the result that the query is supposed to achieve.
I think the crux of the problem is the value of t.employee returned for the GROUP BY, multiple detail rows with a variety of values for t.employee are getting collapsed into a single row for each value of c.centre, and the value of t.employee is from "some row" in the set. (A MySQL-specific non-standard extension allows the query to run without throwing an error, where other RDBMS would throw an error. We can get MySQL behavior more inline with the standard by including ONLY_FULL_GROUP_BY in `sql_mode. But that would just cause the SQL in the question to throw an error.)
Suggested fix (just a guess) is to derived ac and ad for each employee, before doing the GROUP BY, and then aggregating.
(I'm still suspicious of the joins to centre, not being included in the subqueries. Is employee the primary key or a unique key in employees? Is centre functionally dependent on employee? So many questions, too many assumptions.
My guess is that we are after the result returned by a query something like this:
SELECT c.name
, SUM(v.ad) AS `ad`
, SUM(v.ac) AS `ac`
FROM ( -- derive `ad` and `ac` in an inline view before we collapse rows
SELECT ee.employee
, ee.centre
, ( -- derived for each employee
SELECT SUM(d1.duration)
FROM time t1
JOIN dates d1
ON d1.time_id = t1.id
AND d1.date >= NOW() + INTERVAL -12 MONTH
WHERE d1.employee = t.employee
) AS `ad`
, ( -- derived for each employee
SELECT SUM(d2.cost)
FROM time t2
JOIN dates d2
ON d2.time_id = t2.id
AND d2.date >= NOW() + INTERVAL -12 MONTH
WHERE d2.employee = t.employee
) AS `ac`
FROM time t
JOIN employees ee
ON ee.employee = t.employee
WHERE ee.centre in (4792,4804,4834)
GROUP
BY ee.employee
, ee.centre
) v
LEFT
JOIN centres c
ON c.id = v.centre
GROUP
BY v.centre
, c.name