MySQL 14天重置查询

Question

I'm building a basic system that selects 2 staff members at random to support the business for half of the day. I'm really struggling with the database and how I would actually go about completing this task as they've listed certain rules which are making it quite tricky.

Business Rules:

• An engineer can do at most one half-day shift in a day.

• An engineer cannot have half day shifts on consecutive days.

• Each engineer should have completed one whole day of support in any 2 week period.

I'm a real beginner with this, but so far this is how I think of the problem:

Two Tables:

EMPLOYEE:

employee_id (pk)
first_name
last_name

SHIFTS:

shift_id (pk)
employee_id (fk)
shift_hours

SAMPLE DATA:

 1. shift_id = 1, employee_id = 1, shift_hours = 4
 2. shift_id = 2, employee_id = 2, shift_hours = 6

---

 1. employee_id = 1, first_name = steve, second_name = jones
 2. employee_id = 2, first_name = rob, second_name = helen

---

My question is as follows: Based on the data above, what can I query to ensure that I am picking only users from the database that have only worked LESS than 8 hours in the past 14 days (How can I go about this 14 day issue, can there be some kind of "reset" 24 hours after somebody hits 8 the 8 hour mark, is that possible?)

Hopefully my question is clear, I do apologise as I am a bit of a beginner.

Thanks in advance

(This is different from my previous question, please see the bottom, I have merely just copied the explanation of the problem)

Answer 1

First thing i would not necessarily do shift_hours i would do like started_at and ended_at and make them datetime columns. This way you can do date math in your query to derive the amount of time worked, and you can select between specific dates.

With that as the premise maybe the tables look like so:

CREATE TABLE `employee` (
  id INTEGER AUTO_INCREMENT NOT NULL,
  first_name VARCHAR(32) NOT NULL,
  last_name VARCHAR(32) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB;

CREATE TABLE `shift` (
  id INTEGER AUTO_INCREMENT NOT NULL,
  started_at DATETIME NOT NULL,
  ended_at DATETIME NOT NULL,
  employee_id INTEGER,
  PRIMARY KEY (`id`),
  KEY `shift_employee_id` (`employee_id`),
  FOREIGN KEY `shift_employee_id_fk_employee_id` (`employee_id`)
    REFERENCES `employee` (`id`)
    ON DELETE CASCADE
) ENGINE=INNODB;

So now we could query like:

SELECT e.first_name, e.last_name, SUM(ABS(TIMESTAMPDIFF(HOUR, s.started_at, s.ended_at))) as shift_hours
FROM employee e, shift s
WHERE e.id = s.employee_id
AND s.started_at BETWEEN '2018-01-01' AND '2018-01-15'
GROUP BY e.id
HAVING shift_hours < 8;

This would give us only employees who have logged less than 8 hours between the given dates we supply.

SQL fiddle: http://sqlfiddle.com/#!9/280d88/6 (note, i didnt want to generate enough data to use your 14 day rule, but you should get the idea).

The other rules are ones you will want to apply in the logic of your code when assigning shifts. Though you could probably do it in a stored procedure.