Q:

Can you make this query faster?

I'm currently doing a summer job and I have to extend an existing program.
My boss asked me to make a tool for our clients so they can see how much their employees cost, per month. But that's not all. The thing is that a company can have one or more 'societies', or subcompanies. We want know how much an employee costs per society in a company.
These are the table I use:

society: a subcompany with a people_id which contains the name, etc. of the society
timesheet: timesheet entries that contain person and society information
people: all people or contacts in the database
salarystate: contains the salary for a person for a specific month
overhead: overhead cost for a person for a specific month (note that date is a string (!) formatted like this: YYYY-MM-DD)

This query works, but it takes very long time to execute. Is there a way to make it faster?
I select the year and month, get the name of the employee (worker) and the name of the society. Then I select the sum of the minutes the employee has worked (for a specific society). And finally I calculate the cost by checking his salary for that month and the overhead for that month.
SELECT
    YEAR(TS.assigndate) AS timesheet_year,
    MONTH(TS.assigndate) AS timesheet_month,
    CONCAT(TP.name, ' ', TP.firstname) AS worker,
    CONCAT(SP.name, ' ', SP.firstname) AS society,
    (
        SELECT
            SUM(timeunits) AS minutes
        FROM timesheet
        WHERE
            people_id = TP.id AND
            society_id = S.id AND
            MONTH(assigndate) = timesheet_month
    ) AS minutes,
    (
        SELECT (minutes / 60)
    ) AS hours,
    (
        SELECT(OO.hourtarif + SS.hourtarif) AS cost
        FROM salarystate SS, overhead OO
        WHERE
            people_id = TP.id AND
            YEAR(OO.date) = timesheet_year AND
            MONTH(OO.date) = timesheet_month AND
            CONVERT(SUBSTRING(SS.month FROM 1 FOR 4), UNSIGNED) = timesheet_year AND
            CONVERT(SUBSTRING(SS.month, -2), UNSIGNED) = timesheet_month
    ) AS cost,
    (
        SELECT (hours * cost)
    ) AS total_cost
FROM timesheet TS, society S, people SP, people TP
WHERE
    S.id = TS.society_id AND
    SP.id = S.people_id AND
    TP.id = TS.people_id
GROUP BY timesheet_year, timesheet_month, worker, society; 

A:

Now I use temporary tables it goes fast as hell :). This is the code now, if you're interested:
CREATE TEMPORARY TABLE IF NOT EXISTS people_hours (
    people_id INTEGER NOT NULL,
    society_id INTEGER NOT NULL,
    year INTEGER NOT NULL,
    month INTEGER NOT NULL,
    hours DOUBLE NOT NULL,
    PRIMARY KEY(people_id, society_id, year, month)
);

CREATE TEMPORARY TABLE IF NOT EXISTS people_cost (
    people_id INTEGER NOT NULL,
    year INTEGER NOT NULL,
    month INTEGER NOT NULL,
    cost DOUBLE NOT NULL,
    PRIMARY KEY(people_id, year, month)
);

TRUNCATE people_hours;
TRUNCATE people_cost;

INSERT INTO people_hours (people_id, society_id, year, month, hours)
SELECT
    p.id as people_id,
    s.id as society_id,
    YEAR(t.assigndate) as year,
    MONTH(t.assigndate) as month,
    SUM(t.timeunits)/60 as hours
FROM people p, society s, timesheet t
WHERE
    t.society_id = s.id AND
    t.people_id = p.id
GROUP BY year, month, people_id, society_id;

INSERT INTO people_cost (people_id, year, month, cost)
SELECT
    p.id as people_id,
    YEAR(o.date) as cost_year,
    MONTH(o.date) as cost_month,
    SUM(o.hourtarif + s.hourtarif) as cost
FROM people p, salarystate s, overhead o
WHERE
    s.people_id = p.id AND
    CONVERT(SUBSTRING(s.month FROM 1 FOR 4), UNSIGNED) = YEAR(o.date) AND
    CONVERT(SUBSTRING(s.month, -2), UNSIGNED) = MONTH(o.date)
GROUP BY cost_year, cost_month, people_id;

SELECT 
    h.year,
    h.month,
    h.society_id,
    h.hours,
    c.cost,
    (h.hours * c.cost) AS total_cost,
    CONCAT(p.name, ' ', p.firstname) AS employee,
    CONCAT(ps.name, ' ', ps.firstname) AS society
FROM people_hours h, people_cost c, people p, people ps, society s
WHERE
    h.society_id = s.id AND
    h.people_id = p.id AND
    h.people_id = c.people_id AND
    s.people_id = ps.id AND
    h.year = c.year AND
    h.month = c.month
ORDER BY h.year, h.month, h.people_id, h.society_id;

