Getting collections of consecutive dates - mysql

Question

I have a database which stores employees leave. For each day an employee is on leave a new record is entered to the database. What I want to achieve is for someone to enter an employee id and a date range and for each period of absence a record is returned stating date from, date to, duration and also whether it was AM or PM (for half days).
It should look something like (for employee 9999 and dates 2011-08-08 to 2011-09-01):
employee_id | Start | start_am_pm | End | end_am_pm | Duration
9999 | 2011-08-10 | PM | 2011-08-12 | AM | 2
9999 | 2011-09-01 | | 2011-09-01 | | 1
Note: first duration above is 2 because 10th and 12th are both half days and 11th is a full.
Anyway. The query I have works exactly as I would expect, if the From date is not a date that the employee has leave on. Eg, in the above example if I set the from date to 10th, 11th or 12th, it removes that line. It should count the days between the dates specified.
How it currently shows (for employee 9999 and dates 2011-08-11 to 2011-09-01):
employee_id | Start | start_am_pm | End | end_am_pm | Duration
9999 | 2011-09-01 | | 2011-09-01 | | 1
Similar was happening with the To date but I got that fixed. A similar approach didn't work for the From date. Below is my stored procedure.
DELIMITER $$
USE `test`$$
DROP PROCEDURE IF EXISTS `GetLeaveDates`$$
CREATE DEFINER=`root`#`%` PROCEDURE `GetLeaveDates`(pEmpID INT, pDateFrom DATETIME, pDateTo DATETIME)
BEGIN
SELECT
a.start_date,
CASE WHEN a.am_pm = 1 THEN "AM"
WHEN a.am_pm = 2 THEN "PM"
ELSE "" END AS start_am_pm,
CASE WHEN pDateTo > MIN(c.start_date) THEN
MIN(c.start_date)
ELSE
pDateTo
END AS End,
CASE WHEN c.am_pm = 1 THEN "AM"
WHEN c.am_pm = 2 THEN "PM"
ELSE "" END AS start_am_pm,
CASE WHEN a.am_pm = 0 AND c.am_pm = 0 THEN
DATEDIFF(MIN(c.start_date),a.start_date)+1
WHEN (a.am_pm = 0 AND c.am_pm <> 0) OR (c.am_pm = 0 AND a.am_pm <> 0) THEN
DATEDIFF(MIN(c.start_date),a.start_date)+0.5
WHEN a.am_pm <> 0 AND c.am_pm <> 0 THEN
DATEDIFF(MIN(c.start_date),a.start_date)
END
AS Duration
FROM t AS a
LEFT JOIN t AS b ON a.employee_id=b.employee_id AND a.start_date = ADDDATE(b.start_date,1)
LEFT JOIN t AS c ON a.employee_id=c.employee_id AND a.start_date <= c.start_date
LEFT JOIN t AS d ON c.employee_id=d.employee_id AND c.start_date = ADDDATE(d.start_date,-1)
WHERE b.start_date IS NULL AND c.start_date IS NOT NULL AND d.start_date IS NULL
AND a.EMPLOYEE_ID = pEmpID
AND a.START_DATE BETWEEN pDateFrom AND pDateTo
GROUP BY a.employee_id, a.start_date
; END$$
DELIMITER ;

Answer 1

Ok I figured it out and it was quite simple, basically on each of the LEFT JOIN I had to filter by out the start date by the parameters passed in.
I also had to filter by whether the leave was approved, an Approved_DateTime and Approved_By field where filled in if it was approved. Also the calculation of the duration was a bit off in some circumstances. So my stored procedure now looks like:
DELIMITER $$
USE `test`$$
DROP PROCEDURE IF EXISTS `GetLeaveDates`$$
CREATE DEFINER=`root`#`%` PROCEDURE `GetLeaveDates`(pEmpID INT, pDateFrom DATETIME, pDateTo DATETIME, pApproved BOOLEAN)
BEGIN
SELECT
DATE_FORMAT(a.start_date,'%d/%m/%y') AS start,
CASE WHEN a.am_pm = 1 THEN "AM"
WHEN a.am_pm = 2 THEN "PM"
ELSE "" END AS start_am_pm,
DATE_FORMAT(CASE WHEN pDateTo > MIN(c.start_date) THEN
MIN(c.start_date)
ELSE
pDateTo
END, '%d/%m/%y') AS end,
CASE WHEN c.am_pm = 1 THEN "AM"
WHEN c.am_pm = 2 THEN "PM"
ELSE "" END AS end_am_pm,
CASE WHEN a.am_pm = 0 THEN
CASE WHEN c.am_pm = 0 OR c.am_pm = 2 THEN
DATEDIFF(MIN(c.start_date),a.start_date)+1
WHEN c.am_pm = 1 THEN
DATEDIFF(MIN(c.start_date),a.start_date)+0.5
END
WHEN a.am_pm = 1 THEN
CASE WHEN c.am_pm = 0 OR c.am_pm = 2 THEN
DATEDIFF(MIN(c.start_date),a.start_date)+1
WHEN c.am_pm = 1 THEN
DATEDIFF(MIN(c.start_date),a.start_date)+0.5
END
WHEN a.am_pm = 2 THEN
CASE WHEN c.am_pm = 0 OR c.am_pm = 2 THEN
DATEDIFF(MIN(c.start_date),a.start_date)+0.5
WHEN c.am_pm = 1 THEN
DATEDIFF(MIN(c.start_date),a.start_date)
END
END AS Duration
FROM t AS a
LEFT JOIN t AS b ON a.employee_id=b.employee_id AND a.start_date = ADDDATE(b.start_date,1) AND ISNULL(b.approved_datetime) <> pApproved AND b.start_date BETWEEN pDateFrom AND pDateTo
LEFT JOIN t AS c ON a.employee_id=c.employee_id AND a.start_date <= c.start_date AND ISNULL(c.approved_datetime) <> pApproved AND c.start_date BETWEEN pDateFrom AND pDateTo
LEFT JOIN t AS d ON c.employee_id=d.employee_id AND c.start_date = ADDDATE(d.start_date,-1) AND ISNULL(d.approved_datetime) <> pApproved AND d.start_date BETWEEN pDateFrom AND pDateTo
WHERE b.start_date IS NULL AND c.start_date IS NOT NULL AND d.start_date IS NULL
AND a.EMPLOYEE_ID = pEmpID
AND a.START_DATE BETWEEN pDateFrom AND pDateTo
AND ISNULL(a.approved_datetime) <> pApproved
AND a.start_date BETWEEN pDateFrom AND pDateTo
GROUP BY a.employee_id, a.start_date
; END$$
DELIMITER ;