Get week start from week number and year in PostgreSQL - sql

Is there a way to get the true week start (not the first day of the month) based on year and week number in PostgreSQL?
TO_DATE(CONCAT(year,weeknumber), 'yyyyww')
is not producing the right result.

Related

Amazon Redshift- How to get start date of the Week from existing daily date field from the table?

I am trying to get start date of the week from existing daily date field from the same table. For example daily dates from 05/08/2022 to 05/14/2022 , the start of the week date output need to come as 05/08/2022 for all days in the week. week start on Sunday.
Also similar thing require to first date of the Month and quarter(3 month division)
The date_trunc() function performs this operation - https://docs.aws.amazon.com/redshift/latest/dg/r_DATE_TRUNC.html

SQL query to find week number based on days of week in Oracle

I need to find the week number of given date based on days of week.
For example:
I am trying using the below query, but unable to calculate it based on the day.
select
to_char(to_date('20150101','YYYYMMDD')-2,'iw') week_sun_thru_saturday,
to_number(to_char(to_date('20150101','YYYYMMDD')-1,'iw')) -
to_number(to_char( to_date('03-jan-2015','dd-mon-yyyy')+1,'iw')) week_from_03_jan_2015
from dual;

How do I summarise month to date forecast for current month in Power Pivot?

I have a table in a data model that has forecast figures for the next 3 months. What I want to do is to show what the forecast number for the current month to date is.
When I use the DATESMTD function like this:
=CALCULATE(SUM(InternetSales_USD[SalesAmount_USD]),DATESMTD(DateTime[DateKey]))
I get the last month of my data summarised as a total. I assume that is because the DATESMTD function takes the last date in the column and that is 3 months away.
How do I make sure I get this current month MTD total rather then the end of the calendar? The formula should be clever enough to realise I am in May and want the May MTD not the August MTD.
Any ideas?
The way to do this is to do this:
Forecast_Transaction_MTD:=CALCULATE(sum('ATO Online'[2017 Transaction Forecast]), DATESINPERIOD('ATO Online'[Current Year],TODAY(),-day(TODAY()),day))
the last -day(TODAY()) gets the day number for the current day and subtract it from today's date. So, today is the 25 May. the -day(TODAY())),day)) extracts the day (25) and subtracts it from the current date to get me to the 1 May.
The rest of the formula just adds the total for the dates.

How to subtract 13 weeks from a date in PL SQL?

I have a date in sql which will always fall on a Monday and I'm subtracting 13 weeks to get a weekly report. I am trying to get the same 13 week report but for last year's figures as well.
At the moment, I'm using the following:
calendar_date >= TRUNC(sysdate) - 91
which is working fine.
I need the same for last year.
However, when I split this into calendar weeks, there will also be a partially complete week as it will include 1 or 2 days from the previous week. I need only whole weeks.
e.g. the dates that will be returned for last year will be 14-Feb-2015 to 16-May-2015. I need it to start on the Monday and be 16-Feb-2015. This will change each week as I am only interested in complete weeks...
I would do this:
Get the date by substracting 91 days as you're already doing.
Get the number of the day of the week with TO_CHAR(DATE,'d')
Add the number of days until the next monday to the date.
Something like this:
SELECT TO_DATE(TO_DATE('16/05/2015','DD/MM/YYYY'),'DD/MM/YYYY')-91 + MOD(7 - TO_NUMBER(TO_CHAR(TO_DATE(TO_DATE('16/05/2015','DD/MM/YYYY'),'DD/MM/RRRR')-91,'d'))+1,7) d
FROM dual
next_day - returns date of first weekday named by char.
with dates as (select to_date('16/05/2015','DD/MM/YYYY') d from dual)
select
trunc(next_day( trunc(d-91) - interval '1' second,'MONDAY'))
from dates;
I want to get next monday from calculated date. In situation when calculated date is monday i have to move back to previous week ( -1 second).

Access query (SQL) to return records sorted (grouped by) WEEKS

Greetings SQL gurus,
I don't know if you can help me, but I will try. I have several large databases grouped by year (each year in a different database). I want to be able to compare values from a particular week from one year to the next. For example, "show me week 17 of 2008 vs. week 17 of 2002."
I have the following definition of weeks that ideally I would use:
Only 52 weeks each year and 7 days a week (that only takes 364 days),
The first day of the first week starts from January 2nd - which means we do not use January 1st data, and
In leap year, the first day of the first week ALSO starts from the January 2nd plus we skip Feb. 29.
Any ideas?
Thanks in advance.
Best to avoid creating a table because then you have to update and maintain it to get your queries to work.
DatePart('ww',[myDate]) will give you the week number. You may run into some issues though deciding which week belongs to which year - for example if Jan 1 2003 is on Wednesday does the week belong as week 52 in 2002 or week 1 in 2003? Your accounting department will have a day of the week that is your end of week (usually Sat). I usually just pick the year that has the most days in it. DatePart will always count the first week as 1 and in the case of the example above the last week as 53. You may not care that much either way. You can create queries for each year
SELECT DatePart('ww',[myDate]) as WeekNumber,myYearTable.* as WeekNumber
FROM myYearTable
and then join the queries to get your data. You'll loose a couple days at the end of the year if one table has 52 weeks and one has 53 (most will show as 53). Or you can do it by your weekending day - this always gives you Saturday which would push a late week into the following year.
(7-Weekday([myDate]))+[myDate]
then
DatePart('ww',(7-Weekday([myDate]))+[myDate])
Hope that helps
To get the week number
'to get the week number in the year
select datepart( week, datefield)
'to get the week number in the month
select (datepart(dd,datefield) -1 ) / 7 + 1
You don't need to complicate things thinking about leap years, etc. Just compare weeks mon to sun
SInce you havea a specifc defintion of when the week starts that is differnt that the standard used by the db, I think a weeks table is the solution to your problem. For each year create a table that defines the dates contained in each week and the week number. Then by joining to that table as well as the relevant other tables, you can ask for just the data for week 17.
Table structure
Date Week
20090102 1
20090103 1
etc.
I needed to create a query that shows BOTH year AND week numbers, like 2014-52. The year shows correct when you use the Datepart() formula to convert week 53 to week 52 in the previous year, but shows the wrong year for the week that was week 1 previously that should be week 52 now. It show that week as 2015-52 instead of 2014-52.
Furthermore, it sorts the data wrong if you only use only the week number, eg:
2014-1,2014-11,2014-2
To overcome this I created the following query to insert a 0 and also to check for days in week 1 that should still fall under week 52.
ActualWeek: IIf(DatePart("ww",[SomeDate],1,3)=52 And DatePart("ww",[SomeDate])=1, DatePart("yyyy",[SomeDate],1,3)-1,DatePart("yyyy",[SomeDate],1,3)) & "-" & IIf(DatePart("ww",[SomeDate],1,3)<10,"0" & DatePart("ww",[SomeDate],1,3),DatePart("ww",[SomeDate],1,3))