How to Write Sql Query to show total number of leaveDays per months after calculating date difference between startDate and endDate - postgresql

Question

There is Leave Table.It has two columns start-date,end-date.I need to show total Number of Leave Days Per Month. At first I have to calculate totalNumberOfLeave just like:
<table>
<tr>
<th>Person</th>
<th>startDate</th>
<th>endDate</th>
<th>totalNumberOfLeave</th>
</tr>
<tr>
<td>PersonA</td>
<td>2016-08-10</td>
<td>2016-08-12</td>
<td>3</td>
</tr>
<tr>
<td>PersonB</td>
<td>2016-08-31</td>
<td>2016-09-03</td>
<td>4</td>
</tr>
<tr>
<td>PersonC</td>
<td>2016-08-30</td>
<td>2016-09-06</td>
<td>9</td>
</tr>
</table>
After calculating TotalNumberOfLeave,Then I need to show totalNumberOfLeave Per Month just like
<table>
<tr>
<th>Month</th>
<th>NumberOfLeave</th>
</tr>
<tr>
<td>8</td>
<td>6</td>
</tr>
</table>
(Person A takes 2016-08-10,2016-08-11,2016-08-12 as Leave,Person B takes 2016-08-31 as Leave,PersonC takes 2016-08-30,2016-08-31 as Leave in August)
How should I write for showing totalNumberOfLeave Per Month?
DB I use is Postgresql9.3.

Answer 1

SELECT
DATE_PART('MONTH',A.ATTENDANCEDATE) AS MONTH,
SUM(CASE WHEN (A.FULLDAY = '1') THEN 1 ELSE 0.5 END ) AS DURATION
FROM
(
SELECT GENERATE_SERIES(START_DATE,END_DATE, '1 DAY'::INTERVAL) AS ATTENDANCEDATE, IS_FULLDAY AS FULLDAY
FROM LEAVE_TAKEN
) AS A
GROUP BY
DATE_PART('MONTH',A.ATTENDANCEDATE)
ORDER BY
DATE_PART('MONTH',A.ATTENDANCEDATE);