On 03/29/2017 06:19 PM, Shaun Cutts wrote:
When being asked to convert a day of the week, the to_date() function returns
the same day ('0001-01-01 BC’) no matter which day is converted:
# select to_date(‘Monday’, ‘Day’)
'0001-01-01 BC’
# select to_date(‘Tuesday’, ‘Day’)
'0001-01-01 BC’
However, if it were to return a date that was that day of the week, it could be
inverted:
# select extract(dow from '0001-01-01 BC'::date); — this date should be the
result of to_date(‘Sunday’, ‘Day’)
6
# select extract(dow from '0001-01-02 BC'::date); — this date should be the
result of to_date(‘Monday’, ‘Day’)
0
The two examples are not the same. In the second you starting from a
known date and extracting a day number. In the first you are asking for
a day of the week that is not anchored to a date, so any date past or
present that is on that day would fit. I have no problem with
normalizing that to a placeholder date.
….
David tells this is not a bug, but it still seems like a reasonable requirement
on to_date() to me. Is there some reason why this isn’t possible?
What would the requirement be?:
That Day dates w/o a year would be sequential from 0001-01-01 BC?
Or some other Sunday in some other year?
It comes down to what you want "select to_date(‘Monday’, ‘Day’)" to
provide you and for what purpose?
--
Adrian Klaver
adrian.kla...@aklaver.com
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