Calculate age (year, month, day) using DateDiff in stored procedure - sql

I need to show the time that has passed since a specific date in years, months and days, taking leap years/months into account. This has to be within a stored producedure in Firebird 2.1.
I'm struggling with the following code:
SELECT CASE
WHEN :CustomDateTime > CURRENT_DATE THEN 0
WHEN EXTRACT(YEARDAY FROM :CustomDateTime) > EXTRACT(YEARDAY FROM CURRENT_DATE) THEN DATEDIFF(YEAR, :CustomDateTime, CURRENT_DATE) - 1
ELSE DATEDIFF(YEAR, :CustomDateTime, CURRENT_DATE)
END
FROM RDB$DATABASE
INTO :YearDiff;
SELECT CASE
WHEN :CustomDateTime > CURRENT_DATE THEN 0
WHEN (EXTRACT(MONTH FROM :CustomDateTime) = EXTRACT(MONTH FROM CURRENT_DATE))
AND (EXTRACT(YEARDAY FROM :CustomDateTime) > EXTRACT(YEARDAY FROM CURRENT_DATE))
THEN DATEDIFF(MONTH, DATEADD(:YearDiff YEAR TO :CustomDateTime), CURRENT_DATE) - 1
ELSE DATEDIFF(MONTH, DATEADD(:YearDiff YEAR TO :CustomDateTime), CURRENT_DATE)
END
FROM RDB$DATABASE
INTO :MonthDiff;
SELECT CASE
WHEN :CustomDateTime > CURRENT_DATE THEN 0
WHEN (:YearDiff > 0) AND (:MonthDiff > 0) THEN DATEDIFF(DAY, DATEADD(:MonthDiff MONTH TO DATEADD(:YearDiff YEAR TO :CustomDateTime)), CURRENT_DATE)
WHEN (:YearDiff > 0) AND (:MonthDiff = 0) THEN DATEDIFF(DAY, DATEADD(:YearDiff YEAR TO :CustomDateTime), CURRENT_DATE)
WHEN (:YearDiff = 0) AND (:MonthDiff > 0) THEN DATEDIFF(DAY, DATEADD(:MonthDiff MONTH TO :CustomDateTime), CURRENT_DATE)
ELSE DATEDIFF(DAY, :CustomDateTime, CURRENT_DATE)
END
FROM RDB$DATABASE
INTO :DayDiff;
Any ideas on how to fix it?


This is in pl/sql, but you can use this idea for finding the time passed since v_date;
set serveroutput on;
declare
v_date date := '27-APR-16';
PROCEDURE passed(toCheck date) IS
years INTEGER := 0;
months INTEGER := 0;
days INTEGER := 0;
BEGIN
SELECT floor(MONTHS_BETWEEN(sysdate, toCheck)) into months FROM dual;
SELECT SYSDATE - ADD_MONTHS(toCheck, months) INTO days FROM dual;
years := floor(months / 12);
months := months - (years * 12);
dbms_output.put_line('Yers : ' || years || ', ' || ' Months : ' || months || ', Days: ' || days);
END passed;
begin
passed(v_date);
end;

Related

Next workday that not holiday in sql

I have Holiday table that contains all holidays in it.
How can I get next work day from given date in one SQL query and not use FOR Loop like below?
DECLARE
givendate DATE := TO_DATE('2019-07-01', 'YYYY-MM-DD');
out NUMBER := 1;
BEGIN
WHILE out != 0 LOOP
SELECT
COUNT(*)
INTO out
FROM
holiday h
WHERE
trunc(h.holiday_date) = trunc(givendate);
IF out != 0 THEN
givendate := givendate + 1;
END IF;
END LOOP;
DBMS_OUTPUT.put_line(givendate);
END;

SELECT MIN(hd)
FROM (
select TO_DATE('2019-07-01', 'YYYY-MM-DD') as hd from dual
union
select trunc(h.holiday_date + 1)
FROM
holiday h
WHERE
trunc(h.holiday_date) >= TO_DATE('2019-07-01', 'YYYY-MM-DD')
) t left join holiday h2 on trunc(h2.holiday_date) = t.hd
WHERE h2.holiday_date IS NULL;

You may want to use a hierarchical query:
select nvl(max(holiday_date)+1, trunc(sysdate))
from holiday
connect by holiday_date = prior holiday_date + 1
start with holiday_date = trunc(sysdate)
It works like that:
if sysdate is a holiday, it builds a chain of continuous holidays and then returns max holiday_date + 1 as thenext business date
if sysdate is not a holiday, it returns sysdate (nvl() does that when max returns null)
So just replace trunc(sysdate) with your given_date and it should work just as your piece of code.

Business days between two dates with calendar table [duplicate]

I am trying to calculate business days between two dates in Oracle select. I got to the point when my calculation gives most results correct for given dates (I compare it with NETWORKDAYS in excel) but sometimes it varies from 2 days to -2 days - and I don't know why...
Here's my code:
SELECT
((to_char(CompleteDate,'J') - to_char(InstallDate,'J'))+1) - (((to_char(CompleteDate,'WW')+ (52 * ((to_char(CompleteDate,'YYYY') - to_char(InstallDate,'YYYY'))))) - to_char(InstallDate,'WW'))*2) as BusinessDays
FROM TABLE
Thanks!

The solution, finally:
SELECT OrderNumber, InstallDate, CompleteDate,
(TRUNC(CompleteDate) - TRUNC(InstallDate) ) +1 -
((((TRUNC(CompleteDate,'D'))-(TRUNC(InstallDate,'D')))/7)*2) -
(CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SUN' THEN 1 ELSE 0 END) -
(CASE WHEN TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SAT' THEN 1 ELSE 0 END) as BusinessDays
FROM Orders
ORDER BY OrderNumber;
Thanks for all your responses !

I took into account all the different approaches discussed above and came up with a simple query that gives us the number of working days in each month of the year between two dates:
WITH test_data AS
(
SELECT TO_DATE('01-JAN-14') AS start_date,
TO_DATE('31-DEC-14') AS end_date
FROM dual
),
all_dates AS
(
SELECT td.start_date, td.end_date, td.start_date + LEVEL-1 as week_day
FROM test_data td
CONNECT BY td.start_date + LEVEL-1 <= td.end_date)
SELECT TO_CHAR(week_day, 'MON'), COUNT(*)
FROM all_dates
WHERE to_char(week_day, 'dy', 'nls_date_language=AMERICAN') NOT IN ('sun' , 'sat')
GROUP BY TO_CHAR(week_day, 'MON');
Please feel free to modify the query as needed.

Try this:
with holidays as
(
select d from (
select minDate + level -1 d
from (select min(submitDate) minDate, max (completeDate) maxDate
from t)
connect by level <= maxDate - mindate + 1)
where to_char(d, 'dy', 'nls_date_language=AMERICAN') not in ('sun' , 'sat')
)
select t.OrderNo, t.submitDate, t.completeDate, count(*) businessDays
from t join holidays h on h.d between t.submitDate and t.completeDate
group by t.OrderNo, t.submitDate, t.completeDate
order by orderno
Here is a sqlfiddle demo

I changed my example to more readable and to return count of bus. days between. I do not know why you need 'J'- Julian format. All it takes is start/Install and end/Complete dates. You will get correct number of days between 2 dates using this. Replace my dates with yours, add NLS if needed...:
SELECT Count(*) BusDaysBtwn
FROM
(
SELECT TO_DATE('2013-02-18', 'YYYY-MM-DD') + LEVEL-1 InstallDate -- MON or any other day
, TO_DATE('2013-02-25', 'YYYY-MM-DD') CompleteDate -- MON or any other day
, TO_CHAR(TO_DATE('2013-02-18', 'YYYY-MM-DD') + LEVEL-1, 'DY') InstallDay -- day of week
FROM dual
CONNECT BY LEVEL <= (TO_DATE('2013-02-25', 'YYYY-MM-DD') - TO_DATE('2013-02-18', 'YYYY-MM-DD')) -- end_date - start_date
)
WHERE InstallDay NOT IN ('SAT', 'SUN')
/
SQL> 5

I see that marked final solution is not correct always. Suppose, InstallDate is 1st of the month (if falls on Saturday) and CompleteDate is 16th of the month (if falls on Sunday)
In that case, actual Business Days is 10 but the marked query result will give the answer as 12. So, we have to treat this type of cases too, which I used
(CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SAT' AND TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SUN' THEN 2 ELSE 0 END
line to handle it.
SELECT OrderNumber, InstallDate, CompleteDate,
(TRUNC(CompleteDate) - TRUNC(InstallDate) ) +1 -
((((TRUNC(CompleteDate,'D'))-(TRUNC(InstallDate,'D')))/7)*2) -
(CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SUN' THEN 1 ELSE 0 END) -
(CASE WHEN TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SAT' THEN 1 ELSE 0 END) -
(CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SAT' AND TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SUN' THEN 2 ELSE 0 END)as BusinessDays
FROM Orders
ORDER BY OrderNumber;

The accepted solution is quite close but seems wrong in some cases (e.g., 2/1/2015 through 2-28/2015 or 5/1/2015 through 5/31/2015). Here's a refined version...
end_date-begin_date+1 /* total days */
- TRUNC(2*(end_date-begin_date+1)/7) /* weekend days in whole weeks */
- (CASE
WHEN TO_CHAR(begin_date,'D') = 1 AND REMAINDER(end_date-begin_date+1,7) > 0 THEN 1
WHEN TO_CHAR(begin_date,'D') = 8 - REMAINDER(end_date-begin_date+1,7) THEN 1
WHEN TO_CHAR(begin_date,'D') > 8 - REMAINDER(end_date-begin_date+1,7) THEN 2
ELSE 0
END) /* weekend days in partial week */
AS business_days
The part that handles the multiples of 7 (whole weeks) is good. But, when considering the partial week portion, it depends on both the day-of-week offset and the number of days in the partial portion, according to the following matrix...
654321
1N 111111
2M 100000
3T 210000
4W 221000
5R 222100
6F 222210
7S 222221

To just remove sundays and saturdays you can use this
SELECT Base_DateDiff
- (floor((Base_DateDiff + 0 + Start_WeekDay) / 7))
- (floor((Base_DateDiff + 1 + Start_WeekDay) / 7))
FROM (SELECT 1 + TRUNC(InstallDate) - TRUNC(InstallDate, 'IW') Start_WeekDay
, CompleteDate - InstallDate + 1 Base_DateDiff
FROM TABLE) a
Base_DateDiff counts the number of days between the two dates
(floor((Base_DateDiff + 0 + Start_WeekDay) / 7)) counts the number of sundays
(floor((Base_DateDiff + 1 + Start_WeekDay) / 7)) counts the number of saturdays
1 + TRUNC(InstallDate) - TRUNC(InstallDate, 'IW') get 1 for mondays to 7 for sunday

This query can be used to go backward N days from the given date (business days only)
For example, go backward 15 days from 2017-05-17:
select date_point, closest_saturday - (15 - offset + floor((15 - offset) / 6) * 2) from(
select date_point,
closest_saturday,
(case
when weekday_num > 1 then
weekday_num - 2
else
0
end) offset
from (
select to_date('2017-05-17', 'yyyy-mm-dd') date_point,
to_date('2017-05-17', 'yyyy-mm-dd') - to_char(to_date('2017-05-17', 'yyyy-mm-dd'), 'D') closest_saturday,
to_char(to_date('2017-05-17', 'yyyy-mm-dd'), 'D') weekday_num
from dual
))
Some brief explanation: suppose we want to go backward N days from a given date
- Find the closest Saturday that is less than or equal to the given date.
- From the closest Saturday, go back ward (N - offset) days. offset is the number of business days between the closest Saturday and the given date (excluding the given date).
*To go back M days from a Saturday (business days only), use this formula DateOfMonthOfTheSaturday - [M + Floor(M / 6) * 2]

Here is a function that is fast and flexible. You can count any weekday in a date range.
CREATE OR REPLACE FUNCTION wfportal.cx_count_specific_weekdays( p_week_days VARCHAR2 DEFAULT 'MON,TUE,WED,THU,FRI'
, p_start_date DATE
, p_end_date DATE)
RETURN NUMBER
IS
/***************************************************************************************************************
*
* FUNCTION DESCRIPTION:
*
* This function calculates the total required week days in a date range.
*
* PARAMETERS:
*
* p_week_days VARCHAR2 The week days that need to be counted, comma seperated e.g. MON,TUE,WED,THU,FRU,SAT,SUN
* p_start_date DATE The start date
* p_end_date DATE The end date
*
* CHANGE history
*
* No. Date Changed by Change Description
* ---- ----------- ------------- -------------------------------------------------------------------------
* 0 07-May-2013 yourname Created
*
***************************************************************************************************************/
v_date_end_first_date_range DATE;
v_date_start_last_date_range DATE;
v_total_days_in_the_weeks NUMBER;
v_total_days_first_date_range NUMBER;
v_total_days_last_date_range NUMBER;
v_output NUMBER;
v_error_text CX_ERROR_CODES.ERROR_MESSAGE%TYPE;
--Count the required days in a specific date ranges by using a list of all the weekdays in that range.
CURSOR c_total_days ( v_start_date DATE
, v_end_date DATE ) IS
SELECT COUNT(*) total_days
FROM ( SELECT ( v_start_date + level - 1) days
FROM dual
CONNECT BY LEVEL <= ( v_end_date - v_start_date ) + 1
)
WHERE INSTR( ',' || p_week_days || ',', ',' || TO_CHAR( days, 'DY', 'NLS_DATE_LANGUAGE=english') || ',', 1 ) > 0
;
--Calculate the first and last date range by retrieving the first Sunday after the start date and the last Monday before the end date.
--Calculate the total amount of weeks in between and multiply that with the total required days.
CURSOR c_calculate_new_dates ( v_start_date DATE
, v_end_date DATE ) IS
SELECT date_end_first_date_range
, date_start_last_date_range
, (
(
( date_start_last_date_range - ( date_end_first_date_range + 1 ) )
) / 7
) * total_required_days total_days_in_the_weeks --The total amount of required days
FROM ( SELECT v_start_date + DECODE( TO_CHAR( v_start_date, 'DY', 'NLS_DATE_LANGUAGE=english')
, 'MON', 6
, 'TUE', 5
, 'WED', 4
, 'THU', 3
, 'FRI', 2
, 'SAT', 1
, 'SUN', 0
, 0 ) date_end_first_date_range
, v_end_date - DECODE( TO_CHAR( v_end_date, 'DY', 'NLS_DATE_LANGUAGE=english')
, 'MON', 0
, 'TUE', 1
, 'WED', 2
, 'THU', 3
, 'FRI', 4
, 'SAT', 5
, 'SUN', 6
, 0 ) date_start_last_date_range
, REGEXP_COUNT( p_week_days, ',' ) + 1 total_required_days --Count the commas + 1 to get the total required weekdays
FROM dual
)
;
BEGIN
--Verify that the start date is before the end date
IF p_start_date < p_end_date THEN
--Get the new calculated days.
OPEN c_calculate_new_dates( p_start_date, p_end_date );
FETCH c_calculate_new_dates INTO v_date_end_first_date_range
, v_date_start_last_date_range
, v_total_days_in_the_weeks;
CLOSE c_calculate_new_dates;
--Calculate the days in the first date range
OPEN c_total_days( p_start_date, v_date_end_first_date_range );
FETCH c_total_days INTO v_total_days_first_date_range;
CLOSE c_total_days;
--Calculate the days in the last date range
OPEN c_total_days( v_date_start_last_date_range, p_end_date );
FETCH c_total_days INTO v_total_days_last_date_range;
CLOSE c_total_days;
--Sum the total required days
v_output := v_total_days_first_date_range + v_total_days_last_date_range + v_total_days_in_the_weeks;
ELSE
v_output := 0;
END IF;
RETURN v_output;
EXCEPTION
WHEN OTHERS
THEN
RETURN NULL;
END cx_count_specific_weekdays;
/

Here you go...
First check how many days you got in the holiday table, excluding weekend days.
Get business days (MON to FRI) between the 2 dates and after that subtract the holiday days.
create or replace
FUNCTION calculate_business_days (p_start_date IN DATE, p_end_date IN DATE)
RETURN NUMBER IS
v_holidays NUMBER;
v_start_date DATE := TRUNC (p_start_date);
v_end_date DATE := TRUNC (p_end_date);
BEGIN
IF v_end_date >= v_start_date
THEN
SELECT COUNT (*)
INTO v_holidays
FROM holidays
WHERE day BETWEEN v_start_date AND v_end_date
AND day NOT IN (
SELECT hol.day
FROM holidays hol
WHERE MOD(TO_CHAR(hol.day, 'J'), 7) + 1 IN (6, 7)
);
RETURN GREATEST (NEXT_DAY (v_start_date, 'MON') - v_start_date - 2, 0)
+ ( ( NEXT_DAY (v_end_date, 'MON')
- NEXT_DAY (v_start_date, 'MON')
)
/ 7
)
* 5
- GREATEST (NEXT_DAY (v_end_date, 'MON') - v_end_date - 3, 0)
- v_holidays;
ELSE
RETURN NULL;
END IF;
END calculate_business_days;
After that you can test it out, like:
select
calculate_business_days('21-AUG-2013','28-AUG-2013') as business_days
from dual;

There is another easier way, using connect by and dual...
with t as (select to_date('30-sep-2013') end_date, trunc(sysdate) start_date from dual)select count(1) from dual, t where to_char(t.start_date + level, 'D') not in (1,7) connect by t.start_date + level <= t.end_date;
with connect by you get all the dates from start_date till the end_date. Then you can exclude the dates you don't need and count only the needed.

This would return business days:
(CompleteDate-InstallDate)-2*FLOOR((CompleteDate-InstallDate)/7)-
DECODE(SIGN(TO_CHAR(CompleteDate,'D')-
TO_CHAR(InstallDate,'D')),-1,2,0)+DECODE(TO_CHAR(CompleteDate,'D'),7,1,0)-
DECODE(TO_CHAR(InstallDate,'D'),7,1,0) as BusinessDays,

how to find the difference between two dates using Oracle sql by excluding weekends [duplicate]

I am trying to calculate business days between two dates in Oracle select. I got to the point when my calculation gives most results correct for given dates (I compare it with NETWORKDAYS in excel) but sometimes it varies from 2 days to -2 days - and I don't know why...
Here's my code:
SELECT
((to_char(CompleteDate,'J') - to_char(InstallDate,'J'))+1) - (((to_char(CompleteDate,'WW')+ (52 * ((to_char(CompleteDate,'YYYY') - to_char(InstallDate,'YYYY'))))) - to_char(InstallDate,'WW'))*2) as BusinessDays
FROM TABLE
Thanks!

The solution, finally:
SELECT OrderNumber, InstallDate, CompleteDate,
(TRUNC(CompleteDate) - TRUNC(InstallDate) ) +1 -
((((TRUNC(CompleteDate,'D'))-(TRUNC(InstallDate,'D')))/7)*2) -
(CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SUN' THEN 1 ELSE 0 END) -
(CASE WHEN TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SAT' THEN 1 ELSE 0 END) as BusinessDays
FROM Orders
ORDER BY OrderNumber;
Thanks for all your responses !

I took into account all the different approaches discussed above and came up with a simple query that gives us the number of working days in each month of the year between two dates:
WITH test_data AS
(
SELECT TO_DATE('01-JAN-14') AS start_date,
TO_DATE('31-DEC-14') AS end_date
FROM dual
),
all_dates AS
(
SELECT td.start_date, td.end_date, td.start_date + LEVEL-1 as week_day
FROM test_data td
CONNECT BY td.start_date + LEVEL-1 <= td.end_date)
SELECT TO_CHAR(week_day, 'MON'), COUNT(*)
FROM all_dates
WHERE to_char(week_day, 'dy', 'nls_date_language=AMERICAN') NOT IN ('sun' , 'sat')
GROUP BY TO_CHAR(week_day, 'MON');
Please feel free to modify the query as needed.

Try this:
with holidays as
(
select d from (
select minDate + level -1 d
from (select min(submitDate) minDate, max (completeDate) maxDate
from t)
connect by level <= maxDate - mindate + 1)
where to_char(d, 'dy', 'nls_date_language=AMERICAN') not in ('sun' , 'sat')
)
select t.OrderNo, t.submitDate, t.completeDate, count(*) businessDays
from t join holidays h on h.d between t.submitDate and t.completeDate
group by t.OrderNo, t.submitDate, t.completeDate
order by orderno
Here is a sqlfiddle demo

I changed my example to more readable and to return count of bus. days between. I do not know why you need 'J'- Julian format. All it takes is start/Install and end/Complete dates. You will get correct number of days between 2 dates using this. Replace my dates with yours, add NLS if needed...:
SELECT Count(*) BusDaysBtwn
FROM
(
SELECT TO_DATE('2013-02-18', 'YYYY-MM-DD') + LEVEL-1 InstallDate -- MON or any other day
, TO_DATE('2013-02-25', 'YYYY-MM-DD') CompleteDate -- MON or any other day
, TO_CHAR(TO_DATE('2013-02-18', 'YYYY-MM-DD') + LEVEL-1, 'DY') InstallDay -- day of week
FROM dual
CONNECT BY LEVEL <= (TO_DATE('2013-02-25', 'YYYY-MM-DD') - TO_DATE('2013-02-18', 'YYYY-MM-DD')) -- end_date - start_date
)
WHERE InstallDay NOT IN ('SAT', 'SUN')
/
SQL> 5

I see that marked final solution is not correct always. Suppose, InstallDate is 1st of the month (if falls on Saturday) and CompleteDate is 16th of the month (if falls on Sunday)
In that case, actual Business Days is 10 but the marked query result will give the answer as 12. So, we have to treat this type of cases too, which I used
(CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SAT' AND TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SUN' THEN 2 ELSE 0 END
line to handle it.
SELECT OrderNumber, InstallDate, CompleteDate,
(TRUNC(CompleteDate) - TRUNC(InstallDate) ) +1 -
((((TRUNC(CompleteDate,'D'))-(TRUNC(InstallDate,'D')))/7)*2) -
(CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SUN' THEN 1 ELSE 0 END) -
(CASE WHEN TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SAT' THEN 1 ELSE 0 END) -
(CASE WHEN TO_CHAR(InstallDate,'DY','nls_date_language=english')='SAT' AND TO_CHAR(CompleteDate,'DY','nls_date_language=english')='SUN' THEN 2 ELSE 0 END)as BusinessDays
FROM Orders
ORDER BY OrderNumber;

The accepted solution is quite close but seems wrong in some cases (e.g., 2/1/2015 through 2-28/2015 or 5/1/2015 through 5/31/2015). Here's a refined version...
end_date-begin_date+1 /* total days */
- TRUNC(2*(end_date-begin_date+1)/7) /* weekend days in whole weeks */
- (CASE
WHEN TO_CHAR(begin_date,'D') = 1 AND REMAINDER(end_date-begin_date+1,7) > 0 THEN 1
WHEN TO_CHAR(begin_date,'D') = 8 - REMAINDER(end_date-begin_date+1,7) THEN 1
WHEN TO_CHAR(begin_date,'D') > 8 - REMAINDER(end_date-begin_date+1,7) THEN 2
ELSE 0
END) /* weekend days in partial week */
AS business_days
The part that handles the multiples of 7 (whole weeks) is good. But, when considering the partial week portion, it depends on both the day-of-week offset and the number of days in the partial portion, according to the following matrix...
654321
1N 111111
2M 100000
3T 210000
4W 221000
5R 222100
6F 222210
7S 222221

To just remove sundays and saturdays you can use this
SELECT Base_DateDiff
- (floor((Base_DateDiff + 0 + Start_WeekDay) / 7))
- (floor((Base_DateDiff + 1 + Start_WeekDay) / 7))
FROM (SELECT 1 + TRUNC(InstallDate) - TRUNC(InstallDate, 'IW') Start_WeekDay
, CompleteDate - InstallDate + 1 Base_DateDiff
FROM TABLE) a
Base_DateDiff counts the number of days between the two dates
(floor((Base_DateDiff + 0 + Start_WeekDay) / 7)) counts the number of sundays
(floor((Base_DateDiff + 1 + Start_WeekDay) / 7)) counts the number of saturdays
1 + TRUNC(InstallDate) - TRUNC(InstallDate, 'IW') get 1 for mondays to 7 for sunday

This query can be used to go backward N days from the given date (business days only)
For example, go backward 15 days from 2017-05-17:
select date_point, closest_saturday - (15 - offset + floor((15 - offset) / 6) * 2) from(
select date_point,
closest_saturday,
(case
when weekday_num > 1 then
weekday_num - 2
else
0
end) offset
from (
select to_date('2017-05-17', 'yyyy-mm-dd') date_point,
to_date('2017-05-17', 'yyyy-mm-dd') - to_char(to_date('2017-05-17', 'yyyy-mm-dd'), 'D') closest_saturday,
to_char(to_date('2017-05-17', 'yyyy-mm-dd'), 'D') weekday_num
from dual
))
Some brief explanation: suppose we want to go backward N days from a given date
- Find the closest Saturday that is less than or equal to the given date.
- From the closest Saturday, go back ward (N - offset) days. offset is the number of business days between the closest Saturday and the given date (excluding the given date).
*To go back M days from a Saturday (business days only), use this formula DateOfMonthOfTheSaturday - [M + Floor(M / 6) * 2]

Here is a function that is fast and flexible. You can count any weekday in a date range.
CREATE OR REPLACE FUNCTION wfportal.cx_count_specific_weekdays( p_week_days VARCHAR2 DEFAULT 'MON,TUE,WED,THU,FRI'
, p_start_date DATE
, p_end_date DATE)
RETURN NUMBER
IS
/***************************************************************************************************************
*
* FUNCTION DESCRIPTION:
*
* This function calculates the total required week days in a date range.
*
* PARAMETERS:
*
* p_week_days VARCHAR2 The week days that need to be counted, comma seperated e.g. MON,TUE,WED,THU,FRU,SAT,SUN
* p_start_date DATE The start date
* p_end_date DATE The end date
*
* CHANGE history
*
* No. Date Changed by Change Description
* ---- ----------- ------------- -------------------------------------------------------------------------
* 0 07-May-2013 yourname Created
*
***************************************************************************************************************/
v_date_end_first_date_range DATE;
v_date_start_last_date_range DATE;
v_total_days_in_the_weeks NUMBER;
v_total_days_first_date_range NUMBER;
v_total_days_last_date_range NUMBER;
v_output NUMBER;
v_error_text CX_ERROR_CODES.ERROR_MESSAGE%TYPE;
--Count the required days in a specific date ranges by using a list of all the weekdays in that range.
CURSOR c_total_days ( v_start_date DATE
, v_end_date DATE ) IS
SELECT COUNT(*) total_days
FROM ( SELECT ( v_start_date + level - 1) days
FROM dual
CONNECT BY LEVEL <= ( v_end_date - v_start_date ) + 1
)
WHERE INSTR( ',' || p_week_days || ',', ',' || TO_CHAR( days, 'DY', 'NLS_DATE_LANGUAGE=english') || ',', 1 ) > 0
;
--Calculate the first and last date range by retrieving the first Sunday after the start date and the last Monday before the end date.
--Calculate the total amount of weeks in between and multiply that with the total required days.
CURSOR c_calculate_new_dates ( v_start_date DATE
, v_end_date DATE ) IS
SELECT date_end_first_date_range
, date_start_last_date_range
, (
(
( date_start_last_date_range - ( date_end_first_date_range + 1 ) )
) / 7
) * total_required_days total_days_in_the_weeks --The total amount of required days
FROM ( SELECT v_start_date + DECODE( TO_CHAR( v_start_date, 'DY', 'NLS_DATE_LANGUAGE=english')
, 'MON', 6
, 'TUE', 5
, 'WED', 4
, 'THU', 3
, 'FRI', 2
, 'SAT', 1
, 'SUN', 0
, 0 ) date_end_first_date_range
, v_end_date - DECODE( TO_CHAR( v_end_date, 'DY', 'NLS_DATE_LANGUAGE=english')
, 'MON', 0
, 'TUE', 1
, 'WED', 2
, 'THU', 3
, 'FRI', 4
, 'SAT', 5
, 'SUN', 6
, 0 ) date_start_last_date_range
, REGEXP_COUNT( p_week_days, ',' ) + 1 total_required_days --Count the commas + 1 to get the total required weekdays
FROM dual
)
;
BEGIN
--Verify that the start date is before the end date
IF p_start_date < p_end_date THEN
--Get the new calculated days.
OPEN c_calculate_new_dates( p_start_date, p_end_date );
FETCH c_calculate_new_dates INTO v_date_end_first_date_range
, v_date_start_last_date_range
, v_total_days_in_the_weeks;
CLOSE c_calculate_new_dates;
--Calculate the days in the first date range
OPEN c_total_days( p_start_date, v_date_end_first_date_range );
FETCH c_total_days INTO v_total_days_first_date_range;
CLOSE c_total_days;
--Calculate the days in the last date range
OPEN c_total_days( v_date_start_last_date_range, p_end_date );
FETCH c_total_days INTO v_total_days_last_date_range;
CLOSE c_total_days;
--Sum the total required days
v_output := v_total_days_first_date_range + v_total_days_last_date_range + v_total_days_in_the_weeks;
ELSE
v_output := 0;
END IF;
RETURN v_output;
EXCEPTION
WHEN OTHERS
THEN
RETURN NULL;
END cx_count_specific_weekdays;
/

Here you go...
First check how many days you got in the holiday table, excluding weekend days.
Get business days (MON to FRI) between the 2 dates and after that subtract the holiday days.
create or replace
FUNCTION calculate_business_days (p_start_date IN DATE, p_end_date IN DATE)
RETURN NUMBER IS
v_holidays NUMBER;
v_start_date DATE := TRUNC (p_start_date);
v_end_date DATE := TRUNC (p_end_date);
BEGIN
IF v_end_date >= v_start_date
THEN
SELECT COUNT (*)
INTO v_holidays
FROM holidays
WHERE day BETWEEN v_start_date AND v_end_date
AND day NOT IN (
SELECT hol.day
FROM holidays hol
WHERE MOD(TO_CHAR(hol.day, 'J'), 7) + 1 IN (6, 7)
);
RETURN GREATEST (NEXT_DAY (v_start_date, 'MON') - v_start_date - 2, 0)
+ ( ( NEXT_DAY (v_end_date, 'MON')
- NEXT_DAY (v_start_date, 'MON')
)
/ 7
)
* 5
- GREATEST (NEXT_DAY (v_end_date, 'MON') - v_end_date - 3, 0)
- v_holidays;
ELSE
RETURN NULL;
END IF;
END calculate_business_days;
After that you can test it out, like:
select
calculate_business_days('21-AUG-2013','28-AUG-2013') as business_days
from dual;

There is another easier way, using connect by and dual...
with t as (select to_date('30-sep-2013') end_date, trunc(sysdate) start_date from dual)select count(1) from dual, t where to_char(t.start_date + level, 'D') not in (1,7) connect by t.start_date + level <= t.end_date;
with connect by you get all the dates from start_date till the end_date. Then you can exclude the dates you don't need and count only the needed.

This would return business days:
(CompleteDate-InstallDate)-2*FLOOR((CompleteDate-InstallDate)/7)-
DECODE(SIGN(TO_CHAR(CompleteDate,'D')-
TO_CHAR(InstallDate,'D')),-1,2,0)+DECODE(TO_CHAR(CompleteDate,'D'),7,1,0)-
DECODE(TO_CHAR(InstallDate,'D'),7,1,0) as BusinessDays,

Get first (and last) day of month - expression simplification

I need to get date, which was 30 (later I will use also 90 or 18O) days before first day of current (and previous) month. I wrote this, but I think it's unnecessarily complicated, so I come here for help. It's any way how can I simplify this:
ib_encodedate(EXTRACT(YEAR from (dateadd(-30-datediff(day from cast(EXTRACT(MONTH from CURRENT_DATE)
|| '-1-'
|| EXTRACT(YEAR from CURRENT_DATE) as date) to date 'now') DAY to CURRENT_DATE))), EXTRACT(MONTH from (dateadd(-30-datediff(day from cast(EXTRACT(MONTH from CURRENT_DATE)
|| '-1-'
|| EXTRACT(YEAR from CURRENT_DATE) as date) to date 'now') DAY to CURRENT_DATE))),EXTRACT(DAY from (dateadd(-30-datediff(day from cast(EXTRACT(MONTH from CURRENT_DATE)
|| '-1-'
|| EXTRACT(YEAR from CURRENT_DATE) as date) to date 'now') DAY to CURRENT_DATE))))
In database I have dates in double, so I have to use function ib_encodedate to convert date to double and compare with date in database. Function have prototype:
ib_encodedate(INT year, INT month, INT day)
The same I need to write for last day of month.
Thanks for any help.

Seems like you need something like this:
SELECT
DATEADD (-EXTRACT(DAY FROM CURRENT_DATE)+1 DAY TO CURRENT_DATE) AS FIRST_DAY_OF_MONTH,
DATEADD (-30 DAY TO DATEADD (-EXTRACT(DAY FROM CURRENT_DATE)+1 DAY TO CURRENT_DATE)) AS A_MONTH_AGO,
DATEADD (-90 DAY TO DATEADD (-EXTRACT(DAY FROM CURRENT_DATE)+1 DAY TO CURRENT_DATE)) AS THREE_MONTHS_AGO,
DATEADD (-180 DAY TO DATEADD (-EXTRACT(DAY FROM CURRENT_DATE)+1 DAY TO CURRENT_DATE)) AS SIX_MONTHS_AGO
FROM
RDB$DATABASE
Using the function DATEADD from firebird you can easily accomplish this.

First Day of The Date:
select cast(:DATA as date) - extract(day from cast(:DATA as date)) + 1 from RDB$DATABASE
Last Day of The Date:
select cast(:DATA as date) - extract(day from cast(:DATA as date)) + 32 - extract(day from (cast(:DATA as date) - extract(day from cast(:DATA as date)) + 32)) from RDB$DATABASE

Using Firebird 2.5
First Day:
SELECT CAST(EXTRACT(YEAR FROM CURRENT_DATE)||'-'||EXTRACT(MONTH FROM
CURRENT_DATE)||'-01' AS DATE) FROM RDB$DATABASE
Last Day:
SELECT DATEADD (-1 DAY TO DATEADD (1 MONTH TO CAST(EXTRACT(YEAR FROM
CURRENT_DATE)||'-'||EXTRACT(MONTH FROM CURRENT_DATE)||'-01' AS DATE)))
FROM RDB$DATABASE

If you use firebird 1.5 you can create this function which returns the last day of the month of a specified date:
create or alter procedure LAST_DAY_OF_MONTH (
REFERENCE_DATE date)
returns (
LAST_DAY date)
as
declare variable NEXT_DAY date;
declare variable COUNTER integer;
begin
NEXT_DAY = :REFERENCE_DATE;
COUNTER = 0;
while (:COUNTER < 33) do begin
NEXT_DAY = :NEXT_DAY + 1;
if (extract(month from :NEXT_DAY) = extract(month from :REFERENCE_DATE)) then begin
LAST_DAY = :NEXT_DAY;
end
COUNTER = :COUNTER + 1;
end
suspend;
end
Then to call it just execute:
select last_day from last_day_of_month('02-23-2016')
This will return 02-29-2016

select dateadd (month, -1,dateadd (-extract(day from current_date)+1 day to current_date)) First_day_month_ago
from RDB$DATABASE
union all
select dateadd (-extract(day from current_date)+1 day to current_date) First_day_current_month
from RDB$DATABASE

Migrating from MySQL I needed the FIRST_DAY and LAST_DAY functions. Here they are:
CREATE OR ALTER FUNCTION FIRST_DAY(d TIMESTAMP)
RETURNS DATE
AS
BEGIN
RETURN CAST(d - EXTRACT(DAY FROM d) + 1 AS DATE);
END
and
CREATE OR ALTER FUNCTION LAST_DAY(d TIMESTAMP)
RETURNS DATE
AS
BEGIN
RETURN DATEADD(1 MONTH TO FIRST_DAY(d)) - 1;
END
And executing from isql:
SQL> SELECT first_day(CURRENT_TIMESTAMP), last_day(CURRENT_TIMESTAMP) FROM RDB$DATABASE rd;
FIRST_DAY LAST_DAY
=========== ===========
2020-08-01 2020-08-31

but creating a function like this:
create or alter function F_DAYSOFMONTH (
LMONTH integer,
LYEAR integer)
returns integer
as
declare variable LTMPDT DM_DATA;
declare variable LTMPDT2 timestamp;
begin
SELECT CAST(CAST(:lmonth AS VARCHAR(10)) || '/01/' || CAST(:lyear AS VARCHAR(10)) AS TIMESTAMP) FROM RDB$DATABASE INTO :LTMPDT;
LTMPDT2 = dateadd(1 month TO :LTMPDT);
return datediff(DAY FROM :ltmpdt TO :LTMPDT2);;
end^
SET TERM ; ^

CREATE PROCEDURE FIRST_LAST_DAYOFMONTH(COMPARE_DATE TIMESTAMP)
RETURNS (FIRST_DAYOFOMONTH TIMESTAMP,LAST_DAYOFMONTH TIMESTAM)
AS
BEGIN
FIRST_DAYOFMONTH=COMPARE_DATE-(EXTRACT(DAY FROM :COMPARE_DATE)-1);
LAST_DAYOFMONTH=DATEADD(1 MONT TO :COMPARE_DATE)-1;
SUSPEND;
END^

How to calculate the difference in days between dates

I need to calculate the number of days between dates as detailed below using MSSQL
Each month should be considered as if it has 30 days (even if it doesn't)
The difference between 2 January, 2013 to 2 March, 2013 will be
(30-2) + 30 + 2 days
where (30-2) will be for January
30 will be for February
2 will be for March

create or replace function datediff( p_what in varchar2,
p_d1 in date,
p_d2 in date ) return number
as
l_result number;
begin
select (p_d2-p_d1) *
decode( upper(p_what),
'DAY', 1, 'SS', 24*60*60, 'MI', 24*60, 'HH', 24, NULL )
into l_result from dual;
return l_result;
end;
/
This is what I do in Oracle (Courtesy: ASKTOM).
I get either days, hours, minutes or seconds in difference.
In MS SQL, either
PRINT DATEDIFF(DAY, '1/1/2011', '3/1/2011')
This gives the number of times the midnight boundary is crossed between the two dates. You may decide to need to add one to this if you're including both dates in the count - or subtract one if you don't want to include either date.
OR
DECLARE #startdate datetime2 = '2007-05-05 12:10:09.3312722';
DECLARE #enddate datetime2 = '2009-05-04 12:10:09.3312722';
SELECT DATEDIFF(day, #startdate, #enddate);
Using this you can manipulate.

Looks like you want to get a result similar to Oracle's MONTHS_BETWEEN in SQL Server.
This is a SQL function i wrote in Teradata, you probably just have to change EXTRACT to YEAR/MONTH/DAY(date)
REPLACE FUNCTION MONTHS_BETWEEN(date1 DATE, date2 DATE)
RETURNS FLOAT
SPECIFIC months_between_DT
RETURNS NULL ON NULL INPUT
CONTAINS SQL
DETERMINISTIC
COLLATION INVOKER
INLINE TYPE 1
RETURN
(EXTRACT(YEAR FROM date1) * 12 + EXTRACT(MONTH FROM date1))
- (EXTRACT(YEAR FROM date2) * 12 + EXTRACT(MONTH FROM date2))
+ CASE
WHEN EXTRACT(MONTH FROM date2) <> EXTRACT(MONTH FROM date2+1) AND
EXTRACT(MONTH FROM date1) <> EXTRACT(MONTH FROM date1+1)
THEN 0
ELSE (CAST(1 AS FLOAT))/31 * (EXTRACT(DAY FROM date1) - EXTRACT(DAY FROM date2))
END
;
Then you simply multiply the result * 30 and cast it to an INT.