Find Exact number of days between two dates

Question

How can get the exact number of days between two dates?

Answer 1

An example of business days calculation in SQL */
/* The algorythm is: */
/* 1) Take the absolute difference between the dates */
/* to_date('&todate') - to_date('&frdate') */
/* 2) Subtract the weekends (number of weeks in the range */
/* TRUNC(to_date('&todate'),'D') = 1st day of week that */
/* end of period is in */
/* TRUNC(to_date('&frdate'),'D') = Last day of week that */
/* start of period is in */
/* So subtracting these two gives the number of days */
/* between the two dates but including all of the days in */
/* the weeks that the dates start and end in. When this */
/* number is divided by 7 it gives the number of weeks. */
/* Multiplying by 2 gives the number of weekend days.     */
/* 3) Subtract 1 day if the ending date is on a saturday */
/* DECODE(to_char(to_date('&todate'),'D'),7,-1,0) */
/* --> If the day of the week is saturday (7), returns -1 */
/* 4) Subtract 1 day if the start date is on a sunday */
/* DECODE(to_char(to_date('&frdate'),'D'),1,-1) */
/* --> If the day of the week is sunday (1), returns 1 */
/* 5) Add one day to make the range inclusive (The '1 + ' ) */
/* Author: Kenneth Atkins ([email protected]) */
/* http://www.olywa.net/katkins/oratip */
define frdate = '&1'
define todate = '&2'
set verify off
select      
     '&frdate' From_Date
     ,'&todate' To_Date,
     1 + to_date('&todate') - to_date('&frdate') -
     ((TRUNC(to_date('&todate'),'D') - TRUNC(to_date('&frdate'),'D'))/7)*2
     + DECODE(to_char(to_date('&todate'),'D'),7,-1,0)
+ DECODE(to_char(to_date('&frdate'),'D'),1,-1,0) Business_Days
from dual
Here is an example of running the script:
SQL> @busdays 01-AUG-96 15-AUG-96
FROM_DATE TO_DATE BUSINESS_DAYS
01-AUG-96 15-AUG-96 11