Re: is there an immutable function to switch from date to character?
Sorry I pasted in the wrong code, I had wanted a column with the character version of the date (ie., -Mon-DD). Steve Baldwin's hack pointed me in the right direction. Here is the example: create temporary table junk as select now()::date as evtdate; SELECT 1 alter table junk add column chardate text GENERATED ALWAYS AS (cmm_date_to_char(evtdate)) STORED; select * from junk; evtdate | chardate +- 2024-04-24 | 2024-Apr-24 (1 row) where cmm_date_to_char is defined as: create or replace function cmm_date_to_char(i_date in date) returns text immutable language sql as $$ select to _char(i_date, '-Mon-DD') $$; Thanks! On Wed, Apr 24, 2024 at 5:54 PM Tom Lane wrote: > Celia McInnis writes: > > create temporary table junk as select now()::date as evtdate; > > alter table junk add column chardate text GENERATED ALWAYS AS > > (to_char(evtdate,'-Mon-DD')) STORED; > > > ERROR: generation expression is not immutable > > Probably not; I think all the available conversion functions > respond to some combination of datestyle, lc_time, and timezone > settings. (Type date doesn't depend on timezone, but that keeps you > from using anything that shares functionality with timestamptz ... > and your to_char call promotes the date to timestamptz.) > > I find your example not terribly compelling. Why expend storage > space on such a column? > > If you're bound and determined to do it, writing a wrapper > function that's labeled immutable should work: > > =# create function mytochar(date) returns text > strict immutable parallel safe > as $$ begin return to_char($1::timestamp, '-Mon-DD'); end $$ > language plpgsql; > CREATE FUNCTION > =# alter table junk add column chardate text GENERATED ALWAYS AS > (mytochar(evtdate)) STORED; > ALTER TABLE > > It's on you to be sure that the function actually is immutable, > or at least immutable enough for your use-case. I believe my > example is pretty safe: neither datestyle nor timezone should > affect the timestamp-without-timezone variant of to_char(), > and this particular format string doesn't depend on lc_time. > > regards, tom lane >
Re: is there an immutable function to switch from date to character?
Celia McInnis writes: > create temporary table junk as select now()::date as evtdate; > alter table junk add column chardate text GENERATED ALWAYS AS > (to_char(evtdate,'-Mon-DD')) STORED; > ERROR: generation expression is not immutable Probably not; I think all the available conversion functions respond to some combination of datestyle, lc_time, and timezone settings. (Type date doesn't depend on timezone, but that keeps you from using anything that shares functionality with timestamptz ... and your to_char call promotes the date to timestamptz.) I find your example not terribly compelling. Why expend storage space on such a column? If you're bound and determined to do it, writing a wrapper function that's labeled immutable should work: =# create function mytochar(date) returns text strict immutable parallel safe as $$ begin return to_char($1::timestamp, '-Mon-DD'); end $$ language plpgsql; CREATE FUNCTION =# alter table junk add column chardate text GENERATED ALWAYS AS (mytochar(evtdate)) STORED; ALTER TABLE It's on you to be sure that the function actually is immutable, or at least immutable enough for your use-case. I believe my example is pretty safe: neither datestyle nor timezone should affect the timestamp-without-timezone variant of to_char(), and this particular format string doesn't depend on lc_time. regards, tom lane
Re: is there an immutable function to switch from date to character?
On Thu, Apr 25, 2024 at 7:31 AM Celia McInnis wrote: > create temporary table junk as select now()::date as evtdate; > > alter table junk add column chardate text GENERATED ALWAYS AS > (to_char(evtdate,'-Mon-DD')) STORED; > > ERROR: generation expression is not immutable > > Maybe this is a hack but.. b2bcreditonline=# create temporary table junk as select now()::date as evtdate; SELECT 1 b2bcreditonline=# alter table junk add column chardate text GENERATED ALWAYS AS (to_char(evtdate,'-Mon-DD')) STORED; ERROR: generation expression is not immutable b2bcreditonline=# create or replace function date_to_text(i_date in date) returns text immutable language sql as $$ select to_char(i_date, '-MM-DD') $$; CREATE FUNCTION b2bcreditonline=# alter table junk add column chardate text GENERATED ALWAYS AS (date_to_text(evtdate)) STORED; ALTER TABLE b2bcreditonline=# select * from junk; evtdate | chardate + 2024-04-24 | 2024-04-24 (1 row)
is there an immutable function to switch from date to character?
create temporary table junk as select now()::date as evtdate; alter table junk add column chardate text GENERATED ALWAYS AS (to_char(evtdate,'-Mon-DD')) STORED; ERROR: generation expression is not immutable