Create Custom Week Of Field SQL -- Oracle 12c

Question

This is for a query in Oracle 12c

I'm trying to create a "Week Of" field that will use the date field present in the record to assign that record a Week Of date that reflects the start of a week. I want the start of weeks to be Sundays and the end of weeks to be Saturdays.

To give an example of what I mean:

metric_date        metric        value        week_of
01-oct-20          sales         45           27-sep-20
05-oct-20          sales         15           04-oct-20

Where the week of field is always the most recent sunday date. I have tried to modify this SQL Server code to work in Oracle, as it was written for a similar purpose:

SELECT DATEADD(DAY, -DATEDIFF(DAY, 0, [Order Date]) % 7, [Order Date]) AS [Week of]
FROM dbo.your_table_name

Here is my attempt at replicating the code in Oracle:

SELECT distinct
metric_date,
mod(-(to_date('01-jan-1900','dd-mon-yyyy') - trunc(metric_date)),7) + metric_date as week_of

FROM dbo.table

But it does not return the results I want. Are there any obvious differences you can see that I am not accounting for in my replicated code?

Answer 1

You could use next_day() :

select t.*, next_day(metric_date - 7, 'sunday')
from mytable t

Note that the second argument to next_day() is language-dependent. If your database is configured in another language than English, use the local translation of Sunday.

Answer 2

You can use TRUNC with the IW option (which is independent of the language) to truncate the date to Monday and then shift the values by 1 day:

SELECT metric_date,
       TRUNC( metric_date + INTERVAL '1' DAY, 'IW' ) - INTERVAL '1' DAY
         AS sunday_of_week
FROM   table_name

Which, for the sample data:

CREATE TABLE table_name ( metric_date ) AS
SELECT DATE '2020-10-01' + LEVEL - 1
FROM   DUAL
CONNECT BY LEVEL <= 14;

Outputs:

\nMETRIC_DATE |  SUNDAY_OF_WEEK \n:---------- |  :------------- \n01-OCT-20 |  27-SEP-20      \n02-OCT-20 |  27-SEP-20      \n03-OCT-20 |  27-SEP-20      \n04-OCT-20 |  04-OCT-20      \n05-OCT-20 |  04-OCT-20      \n06-OCT-20 |  04-OCT-20      \n07-OCT-20 |  04-OCT-20      \n08-OCT-20 |  04-OCT-20      \n09-OCT-20 |  04-OCT-20      \n10-OCT-20 |  04-OCT-20      \n11-OCT-20 |  11-OCT-20      \n12-OCT-20 |  11-OCT-20      \n13-OCT-20 |  11-OCT-20      \n14-OCT-20 |  11-OCT-20      \n

db<>fiddle here