On 4/9/21 5:24 AM, hubert depesz lubaczewski wrote:
On Fri, Apr 09, 2021 at 07:24:54AM +0000, Niels Jespersen wrote:Hello all Are these two queries exactly eqivalent? The table is partitioned on r_time, which is a timestamptz. The explain plans are not exactly the same. The first wants to scan a partition more than the latter. select f.xx from f where f.r_time >= '2020-10-01 00:00:00+00'::timestamptz and f.r_time < ('2020-10-01 00:00:00+00'::timestamptz + interval '1 month'); select f.xx from f where f.r_time >= '2020-10-01 00:00:00+00'::timestamptz and f.r_time < ('2020-11-01 00:00:00+00'::timestamptz);It depends on timezone. For example, in my timezone: $ select ('2020-10-01 00:00:00+00'::timestamptz + interval '1 month'), '2020-11-01 00:00:00+00'::timestamptz; ?column? │ timestamptz ────────────────────────┼──────────────────────── 2020-11-01 02:00:00+01 │ 2020-11-01 01:00:00+01 (1 row) Please note that there is 1 hour difference. The reason is that somewhere in there we change time due to daylight savings.
That looks like a flaw in how "month" is calculated. Whether or not October is 744 hours (31 days x 24 hours/day) or 743 hours (subtracting the "fall back" hour), one month from 01-Oct-2020 is still 01-Nov-2020.
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