SQlite join same table twice with different "on" statement - sql

Question

I couldn't find answer for my question, and I don't know if my query is correct and this could be a SQLite issue, please help me solve the problem.
I have two tables in my database:
processTable {id}
taskTable {id, processId, amount, done}
There is a many-to-one relation (one process can have multiple tasks assigned). The "amount" and "done" are integer values that provides task progress information. If "done" >= "amount", the task is done. I need to query database to get something like that:
+---------+-----------+------------+
| process | tasksDone | tasksCount |
+---------+-----------+------------+
| 1 | 1 | 3 |
+---------+-----------+------------+
| 2 | 2 | 5 |
+---------+-----------+------------+
Basing on data that I have in my tables:
processTable
+----+
| id |
+----+
| 1 |
+----+
| 2 |
+----+
tasksTable
+----+-----------+--------+------+
| id | processId | amount | done |
+----+-----------+--------+------+
| 1 | 1 | 10 | 10 | <- this task is done
+----+-----------+--------+------+
| 2 | 1 | 15 | 5 |
+----+-----------+--------+------+
| 3 | 1 | 80 | 5 |
+----+-----------+--------+------+
| 4 | 2 | 25 | 0 |
+----+-----------+--------+------+
| 5 | 2 | 60 | 60 | <- this task is done
+----+-----------+--------+------+
| 6 | 2 | 30 | 15 |
+----+-----------+--------+------+
| 7 | 2 | 40 | 40 | <- this task is done
+----+-----------+--------+------+
| 8 | 2 | 100 | 50 |
+----+-----------+--------+------+
So, I wrote this query:
SELECT processTable.id AS process,
COUNT(tasksTableDone.id) AS tasksDone,
COUNT(tasksTableAll.id) AS tasksCount
FROM processTable
LEFT JOIN tasksTable AS tasksTableAll
ON tasksTableAll.processId = processTable.id
LEFT JOIN tasksTable AS tasksTableDone
ON tasksTableDone.processId = processTable.id
AND
tasksTableDone.done >= tasksTableDone.amount
But what I've got is:
+---------+-----------+------------+
| process | tasksDone | tasksCount |
+---------+-----------+------------+
| 1 | 3 | 3 |
+---------+-----------+------------+
| 2 | 5 | 5 |
+---------+-----------+------------+
I was trying run the query with only one join at a time, and everything was working well.
Query with first join only:
SELECT processTable.id AS process,
COUNT(tasksTableAll.id) AS tasksCount
FROM processTable
LEFT JOIN tasksTable AS tasksTableAll
ON tasksTableAll.processId = processTable.id
Result:
+---------+------------+
| process | tasksCount |
+---------+------------+
| 1 | 3 |
+---------+------------+
| 2 | 5 |
+---------+------------+
Query with second join only:
SELECT processTable.id AS process,
COUNT(tasksTableDone.id) AS tasksDone
FROM processTable
LEFT JOIN tasksTable AS tasksTableDone
ON tasksTableDone.processId = processTable.id
AND
tasksTableDone.done >= tasksTableDone.amount
Result:
+---------+-----------+
| process | tasksDone |
+---------+-----------+
| 1 | 1 |
+---------+-----------+
| 2 | 2 |
+---------+-----------+
How to use this two joins within one query to get proper results? I know that instead of JOIN I could use another SELECT, but I think it would be more expensive in the performance meaning.

Answer 1

You can implement a CASE statement with an aggregate:
Version using SUM()
SELECT p.id AS process,
sum(case when t.amount = t.done then 1 else 0 end) AS tasksDone,
count(p.id) AS tasksCount
FROM processTable p
LEFT JOIN tasksTable t
ON t.processId = p.id
group by p.id
See SQL Fiddle with Demo
Version using COUNT():
SELECT p.id AS process,
count(case when t.amount = t.done then 1 else null end) AS tasksDone,
count(p.id) AS tasksCount
FROM processTable p
LEFT JOIN tasksTable t
ON t.processId = p.id
group by p.id
See SQL Fiddle with Demo
Edit, after your comment you can wrap this in a select to get the progress:
select process,
tasksDone,
tasksCount,
(tasksDone / tasksCount) progress
from
(
SELECT p.id AS process,
count(case when t.amount = t.done then 1 else null end) AS tasksDone,
count(p.id) AS tasksCount
FROM processTable p
LEFT JOIN tasksTable t
ON t.processId = p.id
group by p.id
) src