diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/datatype.sgml | 71 | ||||
| -rw-r--r-- | doc/src/sgml/func.sgml | 111 |
2 files changed, 96 insertions, 86 deletions
diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml index 66510ee0315..73e51b0b114 100644 --- a/doc/src/sgml/datatype.sgml +++ b/doc/src/sgml/datatype.sgml @@ -2869,10 +2869,31 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>- </para> <para> - Field values can have fractional parts: for example, <literal>'1.5 + Internally, <type>interval</type> values are stored as three integral + fields: months, days, and microseconds. These fields are kept + separate because the number of days in a month varies, while a day + can have 23 or 25 hours if a daylight savings time transition is + involved. An interval input string that uses other units is + normalized into this format, and then reconstructed in a standardized + way for output, for example: + +<programlisting> +SELECT '2 years 15 months 100 weeks 99 hours 123456789 milliseconds'::interval; + interval +--------------------------------------- + 3 years 3 mons 700 days 133:17:36.789 +</programlisting> + + Here weeks, which are understood as <quote>7 days</quote>, have been + kept separate, while the smaller and larger time units were + combined and normalized. + </para> + + <para> + Input 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 + because <type>interval</type> internally stores only integral fields, + fractional values must be converted into smaller units. Fractional parts of units greater than months are rounded to be an integer number of months, e.g. <literal>'1.5 years'</literal> becomes <literal>'1 year 6 mons'</literal>. Fractional parts of @@ -2922,33 +2943,6 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>- </tgroup> </table> - <para> - Internally <type>interval</type> values are stored as months, days, - 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 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: - -<programlisting> -SELECT EXTRACT(hours from '80 minutes'::interval); - date_part ------------ - 1 - -SELECT EXTRACT(days from '80 hours'::interval); - date_part ------------ - 0 -</programlisting> - - Functions <function>justify_days</function> and - <function>justify_hours</function> are available for adjusting days - and hours that overflow their normal ranges. - </para> - </sect2> <sect2 id="datatype-interval-output"> @@ -2961,6 +2955,23 @@ SELECT EXTRACT(days from '80 hours'::interval); </indexterm> <para> + As previously explained, <productname>PostgreSQL</productname> + stores <type>interval</type> values as months, days, and + microseconds. For output, the months field is converted to years and + months by dividing by 12. The days field is shown as-is. The + microseconds field is converted to hours, minutes, seconds, and + fractional seconds. Thus months, minutes, and seconds will never be + shown as exceeding the ranges 0–11, 0–59, and 0–59 + respectively, while the displayed years, days, and hours fields can + be quite large. (The <link + linkend="function-justify-days"><function>justify_days</function></link> + and <link + linkend="function-justify-hours"><function>justify_hours</function></link> + functions can be used if it is desirable to transpose large days or + hours values into the next higher field.) + </para> + + <para> The output format of the interval type can be set to one of the four styles <literal>sql_standard</literal>, <literal>postgres</literal>, <literal>postgres_verbose</literal>, or <literal>iso_8601</literal>, diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index cf3de80394e..830566028c5 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -9166,7 +9166,8 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}'); </para> <para> Subtract timestamps (converting 24-hour intervals into days, - similarly to <function>justify_hours()</function>) + similarly to <link + linkend="function-justify-hours"><function>justify_hours()</function></link>) </para> <para> <literal>timestamp '2001-09-29 03:00' - timestamp '2001-07-27 12:00'</literal> @@ -9579,35 +9580,35 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}'); <row> <entry role="func_table_entry"><para role="func_signature"> - <indexterm> + <indexterm id="function-justify-days"> <primary>justify_days</primary> </indexterm> <function>justify_days</function> ( <type>interval</type> ) <returnvalue>interval</returnvalue> </para> <para> - Adjust interval so 30-day time periods are represented as months + Adjust interval, converting 30-day time periods to months </para> <para> - <literal>justify_days(interval '35 days')</literal> - <returnvalue>1 mon 5 days</returnvalue> + <literal>justify_days(interval '1 year 65 days')</literal> + <returnvalue>1 year 2 mons 5 days</returnvalue> </para></entry> </row> <row> <entry role="func_table_entry"><para role="func_signature"> - <indexterm> + <indexterm id="function-justify-hours"> <primary>justify_hours</primary> </indexterm> <function>justify_hours</function> ( <type>interval</type> ) <returnvalue>interval</returnvalue> </para> <para> - Adjust interval so 24-hour time periods are represented as days + Adjust interval, converting 24-hour time periods to days </para> <para> - <literal>justify_hours(interval '27 hours')</literal> - <returnvalue>1 day 03:00:00</returnvalue> + <literal>justify_hours(interval '50 hours 10 minutes')</literal> + <returnvalue>2 days 02:10:00</returnvalue> </para></entry> </row> @@ -10040,13 +10041,19 @@ EXTRACT(<replaceable>field</replaceable> FROM <replaceable>source</replaceable>) The <function>extract</function> function retrieves subfields such as year or hour from date/time values. <replaceable>source</replaceable> must be a value expression of - type <type>timestamp</type>, <type>time</type>, or <type>interval</type>. - (Expressions of type <type>date</type> are - cast to <type>timestamp</type> and can therefore be used as - well.) <replaceable>field</replaceable> is an identifier or + type <type>timestamp</type>, <type>date</type>, <type>time</type>, + or <type>interval</type>. (Timestamps and times can be with or + without time zone.) + <replaceable>field</replaceable> is an identifier or string that selects what field to extract from the source value. + Not all fields are valid for every input data type; for example, fields + smaller than a day cannot be extracted from a <type>date</type>, while + fields of a day or more cannot be extracted from a <type>time</type>. The <function>extract</function> function returns values of type <type>numeric</type>. + </para> + + <para> The following are valid field names: <!-- alphabetical --> @@ -10055,7 +10062,8 @@ EXTRACT(<replaceable>field</replaceable> FROM <replaceable>source</replaceable>) <term><literal>century</literal></term> <listitem> <para> - The century + The century; for <type>interval</type> values, the year field + divided by 100 </para> <screen> @@ -10063,17 +10071,13 @@ SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13'); <lineannotation>Result: </lineannotation><computeroutput>20</computeroutput> SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40'); <lineannotation>Result: </lineannotation><computeroutput>21</computeroutput> +SELECT EXTRACT(CENTURY FROM DATE '0001-01-01 AD'); +<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput> +SELECT EXTRACT(CENTURY FROM DATE '0001-12-31 BC'); +<lineannotation>Result: </lineannotation><computeroutput>-1</computeroutput> +SELECT EXTRACT(CENTURY FROM INTERVAL '2001 years'); +<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput> </screen> - - <para> - The first century starts at 0001-01-01 00:00:00 AD, although - they did not know it at the time. This definition applies to all - Gregorian calendar countries. There is no century number 0, - you go from -1 century to 1 century. - - If you disagree with this, please write your complaint to: - Pope, Cathedral Saint-Peter of Roma, Vatican. - </para> </listitem> </varlistentry> @@ -10081,14 +10085,13 @@ SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40'); <term><literal>day</literal></term> <listitem> <para> - For <type>timestamp</type> values, the day (of the month) field - (1–31) ; for <type>interval</type> values, the number of days + The day of the month (1–31); for <type>interval</type> + values, the number of days </para> <screen> SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40'); <lineannotation>Result: </lineannotation><computeroutput>16</computeroutput> - SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute'); <lineannotation>Result: </lineannotation><computeroutput>40</computeroutput> </screen> @@ -10162,10 +10165,8 @@ SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40'); <screen> SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40.12-08'); <lineannotation>Result: </lineannotation><computeroutput>982384720.120000</computeroutput> - SELECT EXTRACT(EPOCH FROM TIMESTAMP '2001-02-16 20:38:40.12'); <lineannotation>Result: </lineannotation><computeroutput>982355920.120000</computeroutput> - SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours'); <lineannotation>Result: </lineannotation><computeroutput>442800.000000</computeroutput> </screen> @@ -10193,7 +10194,8 @@ SELECT to_timestamp(982384720.12); <term><literal>hour</literal></term> <listitem> <para> - The hour field (0–23) + The hour field (0–23 in timestamps, unrestricted in + intervals) </para> <screen> @@ -10228,7 +10230,7 @@ SELECT EXTRACT(ISODOW FROM TIMESTAMP '2001-02-18 20:38:40'); <listitem> <para> The <acronym>ISO</acronym> 8601 week-numbering year that the date - falls in (not applicable to intervals) + falls in </para> <screen> @@ -10245,9 +10247,6 @@ SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02'); different from the Gregorian year. See the <literal>week</literal> field for more information. </para> - <para> - This field is not available in PostgreSQL releases prior to 8.3. - </para> </listitem> </varlistentry> @@ -10256,7 +10255,7 @@ SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02'); <listitem> <para> The <firstterm>Julian Date</firstterm> corresponding to the - date or timestamp (not applicable to intervals). Timestamps + date or timestamp. Timestamps that are not local midnight result in a fractional value. See <xref linkend="datetime-julian-dates"/> for more information. </para> @@ -10289,12 +10288,15 @@ SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5'); <term><literal>millennium</literal></term> <listitem> <para> - The millennium + The millennium; for <type>interval</type> values, the year field + divided by 1000 </para> <screen> SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40'); <lineannotation>Result: </lineannotation><computeroutput>3</computeroutput> +SELECT EXTRACT(MILLENNIUM FROM INTERVAL '2001 years'); +<lineannotation>Result: </lineannotation><computeroutput>2</computeroutput> </screen> <para> @@ -10337,18 +10339,16 @@ SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40'); <term><literal>month</literal></term> <listitem> <para> - For <type>timestamp</type> values, the number of the month - within the year (1–12) ; for <type>interval</type> values, - the number of months, modulo 12 (0–11) + The number of the month within the year (1–12); + for <type>interval</type> values, the number of months modulo 12 + (0–11) </para> <screen> SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40'); <lineannotation>Result: </lineannotation><computeroutput>2</computeroutput> - SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months'); <lineannotation>Result: </lineannotation><computeroutput>3</computeroutput> - SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months'); <lineannotation>Result: </lineannotation><computeroutput>1</computeroutput> </screen> @@ -10379,7 +10379,6 @@ SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40'); <screen> SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40'); <lineannotation>Result: </lineannotation><computeroutput>40.000000</computeroutput> - SELECT EXTRACT(SECOND FROM TIME '17:12:28.5'); <lineannotation>Result: </lineannotation><computeroutput>28.500000</computeroutput> </screen> @@ -10461,6 +10460,20 @@ SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40'); </variablelist> </para> + <para> + When processing an <type>interval</type> value, + the <function>extract</function> function produces field values that + match the interpretation used by the interval output function. This + can produce surprising results if one starts with a non-normalized + interval representation, for example: +<screen> +SELECT INTERVAL '80 minutes'; +<lineannotation>Result: </lineannotation><computeroutput>01:20:00</computeroutput> +SELECT EXTRACT(MINUTES FROM INTERVAL '80 minutes'); +<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput> +</screen> + </para> + <note> <para> When the input value is +/-Infinity, <function>extract</function> returns @@ -10502,7 +10515,6 @@ date_part('<replaceable>field</replaceable>', <replaceable>source</replaceable>) <screen> SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40'); <lineannotation>Result: </lineannotation><computeroutput>16</computeroutput> - SELECT date_part('hour', INTERVAL '4 hours 3 minutes'); <lineannotation>Result: </lineannotation><computeroutput>4</computeroutput> </screen> @@ -10580,16 +10592,12 @@ date_trunc(<replaceable>field</replaceable>, <replaceable>source</replaceable> [ <screen> SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40'); <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 20:00:00</computeroutput> - SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40'); <lineannotation>Result: </lineannotation><computeroutput>2001-01-01 00:00:00</computeroutput> - SELECT date_trunc('day', TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40+00'); <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 00:00:00-05</computeroutput> - SELECT date_trunc('day', TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40+00', 'Australia/Sydney'); <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 08:00:00-05</computeroutput> - SELECT date_trunc('hour', INTERVAL '3 days 02:47:33'); <lineannotation>Result: </lineannotation><computeroutput>3 days 02:00:00</computeroutput> </screen> @@ -10628,7 +10636,6 @@ date_bin(<replaceable>stride</replaceable>, <replaceable>source</replaceable>, < <screen> SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-01-01'); <lineannotation>Result: </lineannotation><computeroutput>2020-02-11 15:30:00</computeroutput> - SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-01-01 00:02:30'); <lineannotation>Result: </lineannotation><computeroutput>2020-02-11 15:32:30</computeroutput> </screen> @@ -10814,16 +10821,12 @@ SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-0 <screen> SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'America/Denver'; <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 19:38:40-08</computeroutput> - SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'America/Denver'; <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 18:38:40</computeroutput> - SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'Asia/Tokyo' AT TIME ZONE 'America/Chicago'; <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 05:38:40</computeroutput> - SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT LOCAL; <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 17:38:40</computeroutput> - SELECT TIME WITH TIME ZONE '20:38:40-05' AT LOCAL; <lineannotation>Result: </lineannotation><computeroutput>17:38:40</computeroutput> </screen> @@ -10928,16 +10931,12 @@ LOCALTIMESTAMP(<replaceable>precision</replaceable>) <screen> SELECT CURRENT_TIME; <lineannotation>Result: </lineannotation><computeroutput>14:39:53.662522-05</computeroutput> - SELECT CURRENT_DATE; <lineannotation>Result: </lineannotation><computeroutput>2019-12-23</computeroutput> - SELECT CURRENT_TIMESTAMP; <lineannotation>Result: </lineannotation><computeroutput>2019-12-23 14:39:53.662522-05</computeroutput> - SELECT CURRENT_TIMESTAMP(2); <lineannotation>Result: </lineannotation><computeroutput>2019-12-23 14:39:53.66-05</computeroutput> - SELECT LOCALTIMESTAMP; <lineannotation>Result: </lineannotation><computeroutput>2019-12-23 14:39:53.662522</computeroutput> </screen> |