Get Friday's Data on Monday

Question

I want to create a query that, when it is run on Monday, it retrieves data from Friday. When it is another weekday, it should retrieve data of previous day. At the moment I created this query, which works perfectly except on Monday:

Select sum(od.shippedqty) as SHIPPEDQTY
from orderdetail od, orders o
Where o.orderkey = od.orderkey
and to_char(o.actualshipdate, 'YYYYMMDD') = to_char(sysdate, 'YYYYMMDD') -1

I have tried to do something with a case function and all kind of tips found on the web, but I did not manage to get it to work. Who can help me.

Answer 1

If this query works OK for you, just change the -1 at the very end with

   - case to_char(sysdate, 'Dy') when 'Mon' then 3 else 1 end

With that said - how are you subtracting 1 from a string? Oracle will convert that string back to a number for you, but that is not going to work correctly as dates.

Rather:

... and o.actualshipdate >= trunc(sysdate) - <expression from above>
    and o.actualshipdate <  trunc(sysdate) - <expression from above> + 1

This is better than using trunc on the left-hand side and comparing to trunc(sysdate) , because it allows the use of an index on actualshipdate (assuming there is one, as there should be if you run queries similar to this one often).

Edit : See MT0's comment below (thank you, MT0!). Of course, he is right; if the query may be used in non-English speaking locales, that may be a problem. Even with my suggested modification to the where clause, there is still a to_char() in the whole thing - in the case expression. That should be written as:

to_char(sysdate, 'Dy', 'nls_date_language = English')

Answer 2

You can use:

CASE TRUNC( your_date ) - TRUNC( your_date, 'IW' )
  WHEN 0 THEN your_date - INTERVAL '3' DAY -- Monday
  WHEN 6 THEN your_date - INTERVAL '2' DAY -- Sunday
         ELSE your_date - INTERVAL '1' DAY -- Tuesday - Saturday
END AS previous_workday