Question

I’ve 4 tables as shown below

doctors

id   name
------------
1   Mathew
2   Praveen
3   Rosie
4   Arjun
5   Denis

doctors_appointments

id  doctors_id    patient_name    contact          date               status
--------------------------------------------------------------------------------------
1   5             Nidhin        9876543210  2012-12-10 15:39:41     Registered
2   5             Sunny         9876543210  2012-12-18 15:39:48     Registered
3   5             Mani          9876543210  2012-12-12 15:39:57     Registered
4   2             John          9876543210  2012-12-24 15:40:09     Registered
5   4             Raj           9876543210  2012-12-05 15:41:57     Registered
6   3             Samuel        9876543210  2012-12-14 15:41:33     Registered
7   2             Louis         9876543210  2012-12-24 15:40:23     Registered
8   1             Federick      9876543210  2012-12-28 15:41:05     Registered
9   2             Sam           9876543210  2012-12-12 15:40:38     Registered
10  4             Sita          9876543210  2012-12-12 15:41:00     Registered

doctors_dutyplan

id   doctor_id    weeks             time           no_of_patients
------------------------------------------------------------------
1       1         3,6,7         9:00am-1:00pm          10
2       2         3,4,5         1:00pm-4:00pm          7
3       3         3,6,7         10:00am-2:00pm         10
4       4         3,4,5,6       8:30am-12:30pm         12
5       5         3,4,5,6,7     9:00am-4:00pm          30

emp_leave

id    empid        leavedate
--------------------------------
1   2   2012-12-05 14:42:36
2   2   2012-12-03 14:42:59
3   3   2012-12-03 14:43:06
4   3   2012-12-06 14:43:14
5   5   2012-12-04 14:43:24

My task is to find all the days in a month in which the doctor is available excluding the leave dates.

My query what is wrote is given below:

SELECT DATE_ADD( '2012-12-01', INTERVAL
ROW DAY ) AS Date,
ROW +1 AS DayOfMonth
FROM (

SELECT @row := @row +1 AS
ROW FROM (

SELECT 0
UNION ALL SELECT 1
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 5
UNION ALL SELECT 6
)t1, (

SELECT 0
UNION ALL SELECT 1
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 5
UNION ALL SELECT 6
)t2, (

SELECT @row := -1
)t3
LIMIT 31
)b
WHERE DATE_ADD( '2012-12-01', INTERVAL
ROW DAY )
BETWEEN '2012-12-01'
AND '2012-12-31'
AND DAYOFWEEK( DATE_ADD( '2012-12-01', INTERVAL
ROW DAY ) ) =2
AND DATE_ADD( '2012-12-01', INTERVAL
ROW DAY ) NOT
IN (

SELECT DATE_FORMAT( l.leavedate, '%Y-%m-%d' ) AS date
FROM doctors_dutyplan d
LEFT JOIN emp_leave AS l ON d.doctor_id = l.empid
WHERE doctor_id =2
)

This works fine for all doctors who took any leave in a particular day in a month (here in the example it is Decemeber 2012). and the result for the above query is shown below:

Date         DayOfMonth
-----------------------
2012-12-10       10
2012-12-17       17
2012-12-24       24
2012-12-31       31

But on the other hand for the doctors who didn’t took any leave , for that my query is showing empty table, example for the doctor Mathew whose id is 1, my query returns an empty result

can anyone please tell a solution for this problem.

Thanks in advance.

Answer 1

Your query is large, but this part looks fishy:

NOT IN (
    SELECT DATE_FORMAT( l.leavedate, '%Y-%m-%d' ) AS date
    FROM doctors_dutyplan d
    LEFT JOIN emp_leave AS l ON d.doctor_id = l.empid
    WHERE doctor_id =2

The left join means a null would be returned for doctor 1. Now, col1 not in (null) does not behave as you may expect. It translates to:

col1 <> null

Which is never true. You could solve this by changing the left join to an inner join, so an empty set instead of null is returned for a doctor without leave.