@@ -2756,15 +2756,18 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>-
27562756 </para>
27572757
27582758 <para>
2759- In the verbose input format, and in some fields of the more compact
2760- input formats, field values can have fractional parts; for example
2761- <literal>'1.5 week'</literal> or <literal>'01:02:03.45'</literal>. Such input is
2762- converted to the appropriate number of months, days, and seconds
2763- for storage. When this would result in a fractional number of
2764- months or days, the fraction is added to the lower-order fields
2765- using the conversion factors 1 month = 30 days and 1 day = 24 hours.
2766- For example, <literal>'1.5 month'</literal> becomes 1 month and 15 days.
2767- Only seconds will ever be shown as fractional on output.
2759+ Field values can have fractional parts: for example, <literal>'1.5
2760+ weeks'</literal> or <literal>'01:02:03.45'</literal>. However,
2761+ because interval internally stores only three integer units (months,
2762+ days, microseconds), fractional units must be spilled to smaller
2763+ units. Fractional parts of units greater than months is truncated to
2764+ be an integer number of months, e.g. <literal>'1.5 years'</literal>
2765+ becomes <literal>'1 year 6 mons'</literal>. Fractional parts of
2766+ weeks and days are computed to be an integer number of days and
2767+ microseconds, assuming 30 days per month and 24 hours per day, e.g.,
2768+ <literal>'1.75 months'</literal> becomes <literal>1 mon 22 days
2769+ 12:00:00</literal>. Only seconds will ever be shown as fractional
2770+ on output.
27682771 </para>
27692772
27702773 <para>
@@ -2808,10 +2811,10 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>-
28082811
28092812 <para>
28102813 Internally <type>interval</type> values are stored as months, days,
2811- andseconds . This is done because the number of days in a month
2814+ andmicroseconds . This is done because the number of days in a month
28122815 varies, and a day can have 23 or 25 hours if a daylight savings
28132816 time adjustment is involved. The months and days fields are integers
2814- while theseconds field can storefractions . Because intervals are
2817+ while themicroseconds field can storefractional seconds . Because intervals are
28152818 usually created from constant strings or <type>timestamp</type> subtraction,
28162819 this storage method works well in most cases, but can cause unexpected
28172820 results: