Return year, quarter, month and week from a date

Question

I use this to convert a date filed to year_week, year_month, year_quarter and year.
But when I use it in views I got problem with queries, they take long time...
Is this the best way to do this?
Select  to_char(rec_date, 'yyyy') || to_char(rec_date, 'IW') As year_week,
        to_char(rec_date, 'yyyy') || to_char(rec_date, 'mm') As year_month,
        to_char(rec_date, 'yyyy') || '0' || to_char(rec_date, 'q') As year_quarter,
        to_char(rec_date, 'yyyy') As year
FROM tbltest

Answer 1

I use this to convert a date filed to year_week, year_month, year_quarter and year.
But when I use it in views I got problem with queries, they take long time...
Is this the best way to do this?There is a big difference in showing a date in a certain format (year, month, quater, whatever) and restrict a selection to a certain date.
My guess is that you try to use the view with something like
SELECT * FROM myView
WHERE year = '2007' and year_month = '07'In this case the view is not able to transport the restriction (month='07') to the underlying column rec_date in your table tbltest.
The workaround is to directly use the date column and stay with a date value on it.
Like
SELECT * FROM myView
WHERE rec_date >= to_date('01072007','dd.mm.yyyy') and
and rec_date < to_date('01082007','dd.mm.yyyy') andA normal index on the column rec_date can be used in this second case. There is also a workaround for the first case useing function based indexes.