Query to retrieve previous working day?

Question

I need to write a query that will retrieve the previous working day. Therefore, it must exclude weekends and holidays.
For example, the previous working day for Saturday, February 19 or Sunday, February 20 would be Friday, February 18. And since Monday, February 21 was a holiday for us then the previous working day would also be Friday, February 18.
I've found some queries that allow me to find the previous working day excluding weekends, but I'm having difficulty with the holidays aspect. We have a table called CORPHOLIDAY that contains a field HOLIDAY that stores the holiday dates.
Can I do this with a simple query? I'm not proficient with Oracle, so any and all help is appreciated. Thanks!

Answer 1

Welcome to the forum!
As Dan said, whenever you have a question, it really helps if you post CREATE TABLE and INSERT statements to create whatever tables you need, so people can re-create the problem and test their ideas. Also post the results you want from that data, and your version of Oracle.
The sample data might be as simple as this:
CREATE TABLE     corpholiday
(     holiday     DATE
INSERT INTO corpholiday (holiday) VALUES (DATE '2011-02-21');Here's one way to get the results you want. You enter a starting date (such as February 22, 2011) and the query produces the last working day before that date (in this case, February 18).
WITH     consecutive_days     AS
     SELECT     TO_DATE ( '22-Feb-2011'     -- Input parameter
               , 'DD-Mon-YYYY'
               ) - LEVEL     AS a_date
     FROM     dual
     CONNECT BY     LEVEL     <= 4     -- 1 + Max. possible non-work days
SELECT     MAX (a_date)     AS prev_work_day
FROM           consecutive_days     c
LEFT OUTER JOIN      corpholiday          h  ON     c.a_date     = h.holiday
WHERE     TO_CHAR ( a_date
          , 'Dy'
          , 'NLS_DATE_LANGUAGE=ENGLISH'     -- If necessary
          )     NOT IN ('Sat', 'Sun')
AND     h.holiday     IS NULL
;What you might really like for this job is a WHILE loop, something that would start at the given date, subtract one, test if that day was a work day, and, if necessary, repeat until it did find a work day. That's how you might do it in a procedural language, like PL/SQL, and that's exactly what a lot of people would do: write a PL/SQL function, that could us a WHILE loop. SQL is a non-procedural language, so it doesn't have anything like a loop. Using a CONNECT BY query, as shown above, we can simulate the behavior of a FOR loop, where we do a fixed number of iterations. The query above works by using CONNECT BY to generate the last 4 dates before the given starting date. What is that magic number 4? It's the worst case of how many consecutive days there can be (at least where I work) that is sure to have at least one work day. Where I work, holidays are always at least a week apart, so the longest you can go without a work day is like the example you gave: a Monday (or Friday) holiday, adjacent to the 2 weekend days. You may need to change the number 4 to something higher if, say, December 25 and 26 were both holidays, or if Good Friday and Easter Monday were both holidays.
As posted, the query above works in Oracle 9 (and up), but it can be modified for earlier versions.
Edited by: Frank Kulash on Feb 23, 2011 8:57 PM
Added explanation