date-arithmetic

Given a date range how to calculate the number of weekends partially or wholly within that range? (A few definitions as requested: take 'weekend' to mean Saturday and Sunday. The date range is inclusive i.e. the end date is part of the range 'wholly or partially' means that any part of the weekend falling within the date range means the whole weekend is counted.) To simplify I imagine you only actually need to know the duration and what day of the week the initial day is... I darn well now it's going to involve doing integer division by 7 and some logic to add 1 depending on the remainder but

I have to calculate all the invoices which have been paid in the first 'N' days of a month. I have two tables . INVOICE: it has the invoice information. The only field which does matter is called 'datePayment' . HOLYDAYS: It is a one column table. Entries at this table are of the form "2009-01-01", 2009-05-01" and so on. I should consider also Saturdays and Sundays (this might be not a problem because I could insert those days at the Hollidays table in order to consider them as hollidays if neccesary) The problem is to calculate which is the 'payment limit'. select count(*) from invoice where

Today, I've encountered an unexplainable result in PostgreSQL 9.6 while running this query: SELECT age('2018-06-30','2018-05-19') AS one, age('2018-07-01','2018-05-20') AS two; Expected results for both columns: 1 mon 11 days . However, only for the interval from 2018-05-19 to 2018-06-30, I get what I expect, while for 2018-05-20 till 2018-07-01 I'll get one day more: 1 mon 12 days I don't get why this is the case and in my understanding, between 2018-05-20 2018-07-01 is just an interval of 1 mon 11 days and the Postgres result here is wrong. I cannot find any in-depth information on how

I have a rather weird problem. I live in denmark and here the first week (Week 1) of 2013 starts the 31th of december 2012 and lasts for 7 days - as weeks normally do :) According to .NET however the 30th of december is Week 52, the 31th is Week 53 and the 1st of January is Week 1. Week 53 lasts for only one day, and Week 1 for 6 days. Clearly this must be wrong (a week consisting of less than 7 days) and certainly is wrong in danish context. Where the 31th of december is Week 1, NOT Week 53. The following code illustrates the problem (CurrentCulture is "da-DK") static void Main(string[] args)

Assume this table: id date ---------------- 1 2010-12-12 2 2010-12-13 3 2010-12-18 4 2010-12-22 5 2010-12-23 How do I find the average intervals between these dates, using MySQL queries only? For instance, the calculation on this table will be ( ( 2010-12-13 - 2010-12-12 ) + ( 2010-12-18 - 2010-12-13 ) + ( 2010-12-22 - 2010-12-18 ) + ( 2010-12-23 - 2010-12-22 ) ) / 4 ---------------------------------- = ( 1 DAY + 5 DAY + 4 DAY + 1 DAY ) / 4 = 2.75 DAY Intuitively, what you are asking should be equivalent to the interval between the first and last dates, divided by the number of dates minus 1.

I'm trying to subtract date from Oracle so it even effect the day as well. For example, if the timestamp is 01/June/2015 00 hours and if I subtract 2 hours, I want to be able to go to to 31/May/2014 22 hours. I tried to_char(sysdate-(2/11), 'MM-DD-YYYY HH24') but it only subtracts the hour; it does not touch the day itself. Others have commented on the (incorrect) use of 2/11 to specify the desired interval. I personally however prefer writing things like that using ANSI interval literals which makes reading the query much easier: sysdate - interval '2' hour It also has the advantage of being