CODEWITHSUNDEEP
sqloracle-databasedatedayofweekweekday
Melanie
Melanie

Reputation: 23

PLSQL - How to find Monday and Friday of the week of a given date

I have spent days trying to figure this out to no avail, so hopefully someone can help me. I have a queried date set which contains several fields including a column of dates. What I want to do is create a new field in my query that tells what the Monday and Friday is for the week of that row's particular date.

So for example; if the date in one of my rows is "1/16/18", the new field should indicate "1/15/18 - 1/19/18".

So basically I need to be able to extract the Monday date (1/15/18) and the Friday date (1/19/18) of the week of 1/16/18 and then concatenate the two with a dash ( - ) in between. I need to do this for every row.

How on earth do I do this? I've been struggling just to figure out how to find the Monday or Friday of the given date...

Upvotes: 2

Views: 17296

Answers (3)

Bob Jarvis - Слава Україні
Bob Jarvis - Слава Україні

Reputation: 50077

You can also use the NEXT_DAY function, as in:

SELECT TRUNC(NEXT_DAY(SYSDATE, 'MON')) - INTERVAL '7' DAY AS PREV_MONDAY,
       TRUNC(NEXT_DAY(SYSDATE, 'FRI'))                    AS NEXT_FRIDAY
  FROM DUAL;

Note that using the above, on weekends the Monday will be the Monday preceding the current date, and the Friday will be the Friday following the current date, i.e. there will be 11 days between the two days.

You can also use

SELECT TRUNC(NEXT_DAY(SYSDATE, 'MON')) - INTERVAL '7' DAY AS PREV_MONDAY,
       TRUNC(NEXT_DAY(SYSDATE, 'MON')) - INTERVAL '3' DAY AS NEXT_FRIDAY
  FROM DUAL;

in which case the Monday and Friday will always be from the same week, but if SYSDATE is on a weekend the Monday and Friday returned will be from the PREVIOUS week.

Upvotes: 1

Aleksej
Aleksej

Reputation: 22969

Assuming that your column is of type date, you can use trunc to get the first day of the week (monday) and then add 4 days to get the friday.

For example:

with yourTable(d) as (select sysdate from dual)
select trunc(d, 'iw'), trunc(d, 'iw') + 4
from yourTable

To format the date as a string in the needed format, you can use to_char; for example:

with yourTable(d) as (select sysdate from dual)
select to_char(trunc(d, 'iw'), 'dd/mm/yy') ||'-'|| to_char(trunc(d, 'iw') + 4, 'dd/mm/yy')
from yourTable

gives 

15/01/2018-19/01/18

Upvotes: 4

shawnt00
shawnt00

Reputation: 17953

There may be a simpler, canonical Oracle method to this but you can still reduce it to a simple calculation on your own either way. I'm going to assume you're dealing with only dates falling Monday through Friday. If you do need to deal with weekend dates then you might have to be more explicit about which logical week they should be attached to.

<date> - (to_char(<date>, 'D') - 2) -- Monday
<date> + (6 - to_char(<date>, 'D')) -- Friday

In principle all you need to do is add/subtract the appropriate number of days based on the current day of week (from 1 - 7). There are some implicit casts going on in there and it would probably be wise to handle those better. You might also want to check into NLS settings to make sure you can rely on to_char() using Sunday as the first day of week.

https://docs.oracle.com/cd/B19306_01/server.102/b14200/sql_elements004.htm

Upvotes: 0

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