MySQL link table with extra fields creates cartesian product - mysql

Question

I'm trying to build an app that besides recording number of sales also maintains the history between a supervisor and his/her team.
CREATE TABLE `emp` (
`id` int(11) NOT NULL,
`nombre` varchar(45) NOT NULL,
`apellido` varchar(45) NOT NULL,
`tl_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `tlFK_idx` (`tl_id`),
CONSTRAINT `tlFK` FOREIGN KEY (`tl_id`) REFERENCES `emp` (`id`)
CREATE TABLE `super` (
`id` int(11) NOT NULL,
`nombre` varchar(45) NOT NULL,
`apellido` varchar(45) NOT NULL,
PRIMARY KEY (`id`)
)
CREATE TABLE `emp_super` (
`emp_id` int(11) NOT NULL,
`super_id` int(11) NOT NULL,
`fecha` date NOT NULL,
PRIMARY KEY (`emp_id`,`super_id`,`fecha`),
KEY `empFK_idx` (`emp_id`),
KEY `superFK_idx` (`super_id`),
CONSTRAINT `empsuperFK` FOREIGN KEY (`emp_id`) REFERENCES `emp` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
CONSTRAINT `super_empFK` FOREIGN KEY (`super_id`) REFERENCES `super` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
)
As you can see, the table emp_super is the link table with the exception of having a date field.
emp_id super_id fecha
101863 101404 2012-10-15
101863 101503 2012-10-01
102403 101404 2012-10-15
102403 101503 2012-10-01
103052 101404 2012-10-15
103052 101503 2012-10-01
103718 101404 2012-10-15
103718 101503 2012-10-01
The key is to keep a record of when a supervisor was assigned to a group, so that when there is any change, the new supervisor would not inherit his group's performance under the previous leader.
I've been working on a query to extract the sales made by a particular group but I immediately noticed that even though I think I'm making all the right connections, I receive a Cartesian product.
Here's the sales table:
CREATE TABLE `sales` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`sale_date` date NOT NULL,
`product_id` int(11) NOT NULL,
`emp_id` int(11) NOT NULL,
`qty` int(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`),
KEY `empFK_idx` (`emp_id`),
KEY `campaignFK_idx` (`product_id`),
CONSTRAINT `empFK` FOREIGN KEY (`emp_id`) REFERENCES `emp_super` (`emp_id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
CONSTRAINT `productFK` FOREIGN KEY (`product_id`) REFERENCES `products` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
)
Normally, when dealing with dates, I try and limit the dates to the main table my data is coming from but in this case I need to also take into account the dates for the employee-supervisor relationship.
My query so far is this:
SELECT s.sale_date,su.id,concat_ws(' ',su.nombre,su.apellido), p.name,e.id,concat_ws(' ',e.nombre,e.apellido), s.qty
from tracker.emp e, tracker.products p, tracker.sales s,tracker.super su, tracker.emp_super es
where e.id = es.emp_id
and su.id = es.super_id
and s.product_id = p.id
and e.id = s.emp_id
and s.sale_date between '2012-10-01' and '2012-10-15'
and es.fecha between '2012-10-01' and '2012-10-15'
order by su.id,p.name,e.id;
If I reduce the dates to the 14, then I receive the correct result because the other supervisor did not join until the 15. Has anyone ever encountered this business requirement: to maintain a record of leadership so that a new leader does not inherit his predecessors achievements or mistakes?
Thank you for any suggestions you might have.

Answer 1

You need to take account of when the supervisory role ended.
This will give you that but I suspect that it will not be very efficient.
SELECT e1.emp_id
,e1.super_id
,e1.fecha
,MIN(DATEADD(DAY, -1, e2.fecha)) AS end
FROM emp_super e1
INNER JOIN
emp_super e2 ON e1.emp_id=e2.emp_id
AND
e1.fecha<e2.fecha
GROUP BY e1.emp_id
,e1.super_id
,e1.fecha
Perhaps an end column on the link table updated by a TRIGGER would be better?