SQL to Return Results from Week 13 Year 2008 (not grouped)

Question

Hi folks,

I'm trying to use a Year-Week format in oracle SQL to return results only from a range of Year-Weeks.

Here's what I'm trying

SELECT * FROM widsys.train trn WHERE trn.WID_DATE>=TO_DATE('2008-13', 'YYYY-IW') AND trn.WID_DATE<=TO_DATE('2008-15', 'YYYY-IW') ORDER BY trn.wid_date

but it shoots this error.

ORA-01820: format code cannot appear in date input format but fails on ORA

Any suggestions on what I can use?

Thanks kindly,

Thomas

Answer 1

How about

select * from widsys.train trn 
  where to_char(trn.wid_date, 'YYYY-IW') =  ?
  order by trn.wid_date

and for ranges

select * from widsys.train trn 
  where to_char(trn.wid_date, 'YYYY-IW') between ? and ?
  order by trn.wid_date

The range will use string comparisons, which works fine if smaller numbers are zero-padded: "2009-08" and not "2009-8". But the 'IW' format does this padding.

Answer 2

You could flip it around and do a string compare.

 SELECT * 
 FROM widsys.train trn 
 WHERE to_char(trn.WID_DATE, 'YYYY-IW') ='2008-13'
 ORDER BY trn.wid_date;

I suppose it makes sense that to_date() doesn't work with IW, as the start of the week is somewhat ambiguous - some locales start the week on Sunday, others Monday, etc. Generating a truncated week of the year, unlike a truncated day, month, or year, would therefore be difficult.

edit:

I agree that the natural sort should suffice, but you got me thinking. How would you compare a given date and a formatted YYYY-IW string? I took a stab at it. This attempt could be fashioned into a function that takes a date and a YYYY-IW formatted varchar, but you would need to replace the hard coded strings and the to_date() function calls, and perform some clean up.
It returns a -1 if the passed in date is before the year/weekofyear, 0 if the date falls within the specified weekofyear, and 1 if it is after. It works on ISO week of year, as does the 'IW' format token.

 select (case 
      when input.day < a.startofweek then -1
      when input.day < a.startofweek+7 then 0
      else 1 end)
 from 
 (select 
 -- //first get the iso offset for jan 1, this could be removed if you didn't want iso 
    (select (max(to_number(to_char(to_date('2008','YYYY') + level,'DDD')))) 
     from dual 
     where to_number(to_char(to_date('2008','YYYY')  + level,'IW')) 
      <2 connect by level <= 6) -6
    +
 -- //next get the days in the year to the month in question   
    (select ((to_number(substr('2008-13', 6,2))-1)*7) from dual) startofweek 
     from dual) a, 
 -- //this is generating a test date
  (select to_number(to_char(to_date('2008-07-19', 'YYYYMMDD'), 'DDD')) day 
    from dual) input, 
  dual

Answer 3

I prefer to create a table for weeks for each year that matches my domains local understanding, but thats just me.