database - ISO-8601 in Postgres: How to insert only year in type date? (incomplete date-time values) -

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the postgres database claims supports iso-8601 standard. in iso-8601 date format "yyyy", i.e. consisting of year, fine , acceptable. can't find way add year postgres database field of type "date". idea if i'm doing wrong or feature missing in postgres?

i've seen other posts advising set date "yyyy-01-01" not want , need (since marks specific day of month of year).

scenario

the scenario following. collecting information on people. many have exact dates. have no dates or years, or year , month no day. have able find people born before year, or after other year. easy if have full date. hoped there feature implemented in postgres handle cases of incomplete dates.

to year of date data type:

select extract(year '2014-01-01'::date) the_year;  the_year  ----------      2014

if need year use smallint check constraint

create table t (     the_year smallint check(         the_year between 0 , extract(year current_date)     ) );  insert t (the_year) values (2030); error:  new row relation "t" violates check constraint "t_the_year_check" detail:  failing row contains (2030).  insert t (the_year) values (2014); insert 0 1

but if store whole date makes no sense separate 3 columns.

note semantics of column application. if column of date type application considers year column means year.

check date/time functions , operators

one solution partial date problem pointed @a_horse in comments create column indicating precision of date

create table t (     the_date date,     the_date_precision varchar(5) );  insert t (the_date, the_date_precision) values (current_date, 'year'), (current_date, 'month'), (current_date, 'day') ;  select     case the_date_precision         when 'year' to_char(the_date, 'yyyy')         when 'month' to_char(the_date, 'yyyy-mm')         else to_char(the_date, 'yyyy-mm-dd')     end the_date t ;   the_date   ------------  2014  2014-02  2014-02-06

the above kiss aproach think next implementation more elegant

create table t (     the_date date,     the_date_precision smallint );  insert t (the_date, the_date_precision) values (current_date, 1), (current_date, 2), (current_date, 3) ;  select     array_to_string(         (             string_to_array(to_char(the_date, 'yyyy-mm-dd'), '-')         )[1:the_date_precision]         , '-'     ) the_date t ;   the_date   ------------  2014  2014-02  2014-02-06

that select expression turned function easier reproduce. or view

create view view_t  select *,     array_to_string(         (             string_to_array(to_char(the_date, 'yyyy-mm-dd'), '-')         )[1:the_date_precision]         , '-'     ) the_date_output t ; select * view_t;   the_date  | the_date_precision | the_date_output  ------------+--------------------+-----------------  2014-02-06 |                  1 | 2014  2014-02-06 |                  2 | 2014-02  2014-02-06 |                  3 | 2014-02-06

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