SQL query to determine Fiscal Week

Question

Hi Experts,
I need to figure out the fiscal week for a specific datetime field based on the following requirements:
1. A week Starts on Saturday and Ends on Friday.
2. If Feb 1st of a given year is a Saturday, then week 1 will run from February 1st to February 7.
3. If Feb 1st is not on a Saturday, then week 1 starts on the previous Saturday and ends on the first Friday of February
Example 1: February 1st 2011 is on a tuesday so Week 1 will be from Jan 29th (Saturday) to February 4 (Friday). Week 52 of 2011 will be from Jan 21, 2012 (Saturday) to Jan 27, 2012 (Friday)
Example 2: February 1st 2014 is on a Saturday so Week 1 will be from February 1st to February 7.
I am looking for some sql or pl sql to get the week number. Any help will be greatly appreciated

Answer 1

Hi,
Welcome to the forum!
Here's a PL/SQL function that returns the beginning of the fiscal year which contains a given date, in_date:
CREATE OR REPLACE FUNCTION     fiscal_year_begin
(       in_date       IN   DATE     DEFAULT SYSDATE
RETURN     DATE
DETERMINISTIC
AS
     return_date          DATE;
     next_fiscal_year_begin     DATE;
BEGIN
     return_date     := NEXT_DAY ( ADD_MONTHS ( TRUNC ( ADD_MONTHS (in_date, -1)
                                                , 'YEAR'
                                , 1
                               ) - 7
                         , 'SATURDAY'
     IF  TO_CHAR (in_date, 'MM-DD') BETWEEN '01-26'
                                         AND     '01-31'
     THEN
          next_fiscal_year_begin := fiscal_year_begin (in_date + 7);
          IF  in_date >= next_fiscal_year_begin
          THEN
               return_date := next_fiscal_year_begin;
          END IF;
     END IF;
     RETURN     return_date;
END     fiscal_year_begin
/Here's how it works:
First, it finds the Saturday on or before February 1 in the same calendar year as in_date (or, if in_date is in January, the previous calendar year). In most cases, this will be the beginning of the fiscal year.
The only exceptions are the days between January 26 amd January 31, inclusive. These days could be in the following fiscal year, so we check when that fiscal year begins and, if that date is less than in_date, the later date will be the one returned.
To find the week number of a given date a_date, you can use this formula:
1 + FLOOR ( (a_date - fiscal_year_begin (a_date))
          / 7
       )which finds how may days have passed since the beginning of the fiscal year, dvides by 7 to get the number of completed weeks (0-52), and adds 1 to get the number of the week in progress.
You may want to write another function that does that forumula
You could do the whole job in pure SQL, but it would be messy, and you'd have to copy that messy calculation in every query that used the fiscal year, which I imagine will be a lot of places.
If the PL/SQL function proves to be too slow, you could use it to populate a table that contained the fiscal year starting points for all years in which you might be interested, and join to that table. You could also include every week in that table.
Here's some code I wrote to test the function:
CREATE TABLE table_x
AS
SELECT     DATE '2011-01-26' AS a_date     FROM dual     UNION ALL
SELECT     DATE '2011-01-31'              FROM dual     UNION ALL
SELECT     DATE '2011-02-01'              FROM dual     UNION ALL
SELECT     DATE '2011-02-02'              FROM dual     UNION ALL
SELECT     DATE '2011-02-08'              FROM dual;
INSERT INTO  table_x (a_date)
WITH   cntr     AS
     SELECT     LEVEL     AS n
     FROM     dual
     CONNECT BY     LEVEL <= 10
SELECT     ADD_MONTHS (x.a_date, 12 * c.n)
FROM             table_x    x
CROSS JOIN        cntr           c
ALTER SESSION     SET NLS_DATE_FORMAT     = 'DD-Mon-YYYY Day';
SELECT     a_date
,     fiscal_year_begin (a_date)     AS year
,     1 + FLOOR ( (a_date - fiscal_year_begin (a_date))
                / 7
            )               AS week
FROM     table_x
ORDER BY  a_date;Output:
A_DATE                YEAR                        WEEK
26-Jan-2011 Wednesday 30-Jan-2010 Saturday          52
31-Jan-2011 Monday    29-Jan-2011 Saturday           1
01-Feb-2011 Tuesday   29-Jan-2011 Saturday           1
02-Feb-2011 Wednesday 29-Jan-2011 Saturday           1
08-Feb-2011 Tuesday   29-Jan-2011 Saturday           2
26-Jan-2012 Thursday  29-Jan-2011 Saturday          52
31-Jan-2012 Tuesday   28-Jan-2012 Saturday           1
01-Feb-2012 Wednesday 28-Jan-2012 Saturday           1
02-Feb-2012 Thursday  28-Jan-2012 Saturday           1
08-Feb-2012 Wednesday 28-Jan-2012 Saturday           2
26-Jan-2021 Tuesday   01-Feb-2020 Saturday          52
31-Jan-2021 Sunday    30-Jan-2021 Saturday           1
01-Feb-2021 Monday    30-Jan-2021 Saturday           1
02-Feb-2021 Tuesday   30-Jan-2021 Saturday           1
08-Feb-2021 Monday    30-Jan-2021 Saturday           2Whenever you post a question on this forum, it helps if you also post some sample data (CREATE TABLE and INSERT statements) and the results you want from that data, like I just did.