>>>> 2013/05/24 09:49 -0400, shawn green >>>>
Or we could coerce datetime values back to their date values when both are
being used. The trick now becomes choosing between rounding the datetime value
(times past noon round to the next date) or do we use the floor() function all
the time.
<<<<<<<<
This is simply wrong. Timestamps are not numbers: we do not add timestamps, and
when we subtract them we do not consider the difference something of the same
type. Therefore, one does well to be wary when applying to a timestamp the
notion "rounding".
But containment generally applys: an event on MAY 25th from 1pm to 4pm is
within May 25th, which is within May, .... When containment fails, then there
is trouble: what is the first weekend of August? or the first week of August?
better to say, the weekend or week of August 1st, or 2d, or ...; "day" is a
"common divisor" to calendar-month, weekend, and week.
Therefore, when I learnt that in version 4 MySQL had gone from interpreting a
comparison between DATE and a finer timestamp by the DATE to interpreting it by
the finer timestamp I believed that MySQL was going the wrong way--that MySQL
had gone from a realization of an intuitive sense of containing, as above, to
one on which too much thought had been expended, with a loss of intuitive sense.
I consider the change of 2013/5/25-13 to 2013/5/25 to be truncation, not any
sort of rounding; that is, it is a matter of notation, but one which intuitivly
expresses containment.
These notions sometimes change over the years, and by nation. When the first
public striking clock was set up in Milan, it pointed to hours I through XXIV,
with sunset falling within the 24th hour--that is, the 24th hour ends with 24
o'clock s being struck. This persists to this day in the German expression
"viertel sechs", which means that the sixth hour is one-fourth over, or, as we
would say it, "quarter after five". (Like expressions are found amongst the
Germans s neighbors, but in English never took root.) Nowadays we are are more
inclined to associate both "quarter after five" and "quarter to six"
("dreiviertel sechs") with 5 o'clock than 6 o'clock; this accompanies the
change of notation from 1 through 24 to 0 through 23.
I find MySQL s automatic conversion sometimes to be downright screwy; (version
5.5.8) consider "SELECT NULL" and "SELECT NULL UNION SELECT NULL"; in one of my
views there is a complex wholly numeric expression that becomes "varbinary(32)".
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