rdelaage/postgresql
1
0
Fork 0
mirror of https://git.postgresql.org/git/postgresql.git synced 2024-10-04 19:36:53 +02:00
Code Issues Packages Projects Releases Wiki Activity

doc: interval spill method for units greater than months

Browse Source 
Units are _truncated_ to months, but only in back branches since the
recent commit.

Reported-by: Bryn Llewellyn

Discussion: https://postgr.es/m/BDAE4B56-3337-45A2-AC8A-30593849D6C0@yugabyte.com

Backpatch-through: 9.6 to 14
This commit is contained in:
Bruce Momjian 2021-08-03 12:17:57 -04:00
parent 3d2b6cd6f6
commit 8f203c649f
1 changed files with 14 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
doc/src/sgml/datatype.sgml
View File

@ -2699,15 +2699,18 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>-
</para>
<para>
In the verbose input format, and in some fields of the more compact
input formats, field values can have fractional parts; for example
<literal>'1.5 week'</literal> or <literal>'01:02:03.45'</literal>. Such input is
converted to the appropriate number of months, days, and seconds
for storage. When this would result in a fractional number of
months or days, the fraction is added to the lower-order fields
using the conversion factors 1 month = 30 days and 1 day = 24 hours.
For example, <literal>'1.5 month'</literal> becomes 1 month and 15 days.
Only seconds will ever be shown as fractional on output.
Field values can have fractional parts: for example, <literal>'1.5
weeks'</literal> or <literal>'01:02:03.45'</literal>. However,
because interval internally stores only three integer units (months,
days, microseconds), fractional units must be spilled to smaller
units. Fractional parts of units greater than months is truncated to
be an integer number of months, e.g. <literal>'1.5 years'</literal>
becomes <literal>'1 year 6 mons'</literal>. Fractional parts of
weeks and days are computed to be an integer number of days and
microseconds, assuming 30 days per month and 24 hours per day, e.g.,
<literal>'1.75 months'</literal> becomes <literal>1 mon 22 days
12:00:00</literal>. Only seconds will ever be shown as fractional
on output.
</para>
<para>
@ -2751,10 +2754,10 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>-
<para>
Internally <type>interval</type> values are stored as months, days,
and seconds. This is done because the number of days in a month
and microseconds. This is done because the number of days in a month
varies, and a day can have 23 or 25 hours if a daylight savings
time adjustment is involved. The months and days fields are integers
while the seconds field can store fractions. Because intervals are
while the microseconds field can store fractional seconds. Because intervals are
usually created from constant strings or <type>timestamp</type> subtraction,
this storage method works well in most cases, but can cause unexpected
results: