Question

(query updated for cdhowie comments)

Here’s the situation.
I want to “count the number of tasks assigned to each worker within kind 1,2 of task location AND kind 3,4 of task department”.

Suppose I have the following tables

Task : id, Name
Task_Worker_Combi : Task_id, Worker_id
Worker : id, Name
Task_Location_Combi : Task_id, Location_id
Task_Department_Combi : Task_id, Department_id
Location : id, Name
Department : id, Name

I got as far as the following:(however since it takes forever there must be something wrong with the query)

SELECT W.id, W.Name, COUNT(TWC.Task_id) AS Count
FROM Worker AS W
LEFT JOIN Task_Worker_Combi AS TWC
    ON (W.id=TWC.Worker_id)
WHERE W.id>0 AND TWC.Task_id IN 
(
    SELECT T.id
    FROM Task as T
    LEFT JOIN (Task_Location_Combi AS TLC, Task_Department_Combi AS TDC) 
        ON (T.id=TLC.Task_id AND T.id=TDC.Task_id)
    WHERE 1 AND TLC.Location_id IN (1,2) AND TDC.Department_id IN (3,4)
    GROUP BY T.id
)
GROUP BY W.id
ORDER BY W.Name

Without this subquery it returns “the number of tasks assigned to each worker unconditionally” fine.

AND TWC.Task_id IN 
(
    SELECT T.id
    FROM Task as T
    LEFT JOIN (Task_Location_Combi AS TLC, Task_Department_Combi AS TDC) 
        ON (T.id=TLC.Task_id AND T.id=TDC.Task_id)
    WHERE 1 AND TLC.Location_id IN (1,2) AND TDC.Department_id IN (3,4)
    GROUP BY T.id
)

Where went wrong, and how would you rewrite this query to efficiently work? Please help me somebody. I’m stuck here for over a week now!

The actual query is the following. (assume Job as Task and Worker as Industry from above simplified query)

EXPLAIN SELECT id, Name, COUNT( J.Industry ) AS Count
FROM industry_db.industry AS I
LEFT JOIN job_db.industry AS J ON ( I.id = J.Industry ) 
WHERE I.id >0
AND J.Job
IN (

SELECT t1.id
FROM job_db.job AS t1
LEFT JOIN (
company_db.company AS t2, job_db.industry AS t3, location_db.city AS t4, job_db.function AS t5, job_db.tag AS t6, job_db.degree AS t7, location_db.state AS t8, location_db.group AS t9
) ON ( t1.Company = t2.id
AND t1.id = t3.Job
AND t1.City = t4.id
AND t1.id = t5.Job
AND t1.id = t6.Job
AND t1.id = t7.Job
AND t1.State = t8.id
AND t1.State_Group = t9.id ) 
WHERE 1 
AND t1.Open = '1'
GROUP BY t1.id)
GROUP BY id
HAVING Count >0
ORDER BY Name

And the Explain result from phpmyadmin is the following.

id  select_type  table  type  possible_keys  key  key_len  ref  rows  Extra  
1 PRIMARY I range PRIMARY,id PRIMARY 1 NULL 39 Using where; Using temporary; Using filesort 
1 PRIMARY J ref Industry Industry 1 industry_db.I.id 403 Using where 
2 DEPENDENT SUBQUERY t1 index NULL PRIMARY 4 NULL 2868 Using where 
2 DEPENDENT SUBQUERY t9 eq_ref PRIMARY PRIMARY 1 job_db.t1.State_Group 1 Using index 
2 DEPENDENT SUBQUERY t2 eq_ref PRIMARY PRIMARY 2 job_db.t1.Company 1 Using index 
2 DEPENDENT SUBQUERY t8 eq_ref PRIMARY PRIMARY 1 job_db.t1.State 1 Using index 
2 DEPENDENT SUBQUERY t4 eq_ref PRIMARY PRIMARY 4 job_db.t1.City 1 Using index 
2 DEPENDENT SUBQUERY t7 ref PRIMARY PRIMARY 4 job_db.t1.id 1 Using index 
2 DEPENDENT SUBQUERY t3 ref Job Job 4 job_db.t1.id 1 Using index 
2 DEPENDENT SUBQUERY t5 ref PRIMARY PRIMARY 4 job_db.t7.Job 1 Using index 
2 DEPENDENT SUBQUERY t6 ref PRIMARY PRIMARY 4 job_db.t7.Job 2 Using index 

Answer 1

Try this:

SELECT w.id, w.Name, COUNT( tw.Task_id )
FROM Worker AS w
LEFT JOIN Task_Worker_Combi AS tw
ON(
  w.id = tw.Worker_id AND
  EXISTS( SELECT Task_id FROM Task_Location_Combi
            WHERE Task_id = tw.TaskId AND Location_id IN(1, 2) ) AND
  EXISTS( SELECT Task_id FROM Task_Department_Combi
            WHERE Task_id = tw_TaskId AND Department_id IN(3, 4) )
)