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<chapter id="datatype">

<title id="datatype-title">Data Types</title>

Internally <type>interval</> values are stored as months, days,

and seconds. 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. Because intervals are usually created

from constant strings or <type>timestamp</> subtraction, this

storage method works well in most cases. Functions

time adjustment is involved. The months and days fields are integers

while the seconds field can store fractions. Because intervals are

usually created from constant strings or <type>timestamp</> subtraction,

this storage method works well in most cases. Functions

<function>justify_days</> and <function>justify_hours</> are

available for adjusting days and hours that overflow their normal

ranges.

</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'</> or <literal>'01:02:03.45'</>. 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'</> becomes 1 month and 15 days.

Only seconds will ever be shown as fractional on output.

</para>

</sect2>

<sect2 id="datatype-interval-output">