查找日期范围之间的差距SQL Oracle

Question

l want to get the gap between dates range via SQL query lets see the situation:

l have table employees like : Every month the employee deserve payment

 ID  Name     From_date    To_date    Paid_Amount`

  1    ali     01/01/2002  31/01/2002    300
  2    ali     01/02/2002  28/02/2002    300
  3    ali     01/04/2002  30/04/2002    300
  4    ali     01/05/2002  31/05/2002    300
  5    ali     01/07/2002  31/07/2002    300

Now, we notice there are no payments in March and June
so, how by SQL query I can't get these months ??

Answer 1

Try this,

with mine(ID,Name,From_date,To_date,Paid_Amount) as
(
 select  1,'ali','01/01/2002','31/01/2002',300 from dual union all
 select  2,'ali','01/02/2002','28/02/2002',300 from dual union all
 select  3,'ali','01/04/2002','30/04/2002',300 from dual union all
 select  4,'ali','01/05/2002','31/05/2002',300 from dual union all
 select  5,'ali','01/07/2002','31/07/2002',300 from dual
 ),
 gtfirst (fromdt,todt) as (
       select min(to_Date(from_Date,'dd/mm/yyyy')) fromdt,max(to_Date(to_Date,'dd/mm/yyyy')) todt from mine
 ),
 dualtbl(first,last,fromdt,todt) as
 (
     select * from(select TRUNC(ADD_MONTHS(fromdt, rownum-1), 'MM') AS first,TRUNC(LAST_DAY(ADD_MONTHS(fromdt, rownum-1))) AS last,fromdt,todt from gtfirst connect by level <=12)
     where first between fromdt and todt and last between fromdt and todt
 )
select to_char(first,'month') no_payment_date from dualtbl where first not in (select to_Date(from_Date,'dd/mm/yyyy') from mine)
and first not in (select to_Date(to_date,'dd/mm/yyyy') from mine)

Answer 2

If you want to get the date difference between one payment date and the previous payment date and the ID field is sequential, then you may simply join back to the table and select the previous row.

SELECT X.From_date, Y.From_date, Y.From_date - X.From_date Difference
FROM Employees X
LEFT OUTER JOIN Employees Y ON Y.ID = X.ID - 1

If the ID field is not sequential, then you can use a similar method, but build a temporary table with a row index that you can use to join back to the previous payment.