Re: ERROR: functions in index expression must be marked IMMUTABLE

On 26 February 2017 at 16:09, Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
wrote:

> On 02/26/2017 07:56 AM, Geoff Winkless wrote:
> > On 26 February 2017 at 10:09, Sven R. Kunze <srkunze(at)mail(dot)de
> > <mailto:srkunze(at)mail(dot)de>>wrote:
> >
> > >>># create index docs_birthdate_idx ON docs using btree
> > (((meta->>'birthdate')::date));
> > ERROR: functions in index expression must be marked IMMUTABLE
> >
> > So, what is the problem here?
> >
> >
> > ​Date functions are inherently not immutable because of timezones. Your
> > solution of using to_timestamp doesn't help because it automatically
> > returns a value in WITH TIMESTAMP. Do you get anywhere by using
> > "::timestamp without time zone" instead, as suggested here?
>
> ​Of course I meant "WITH TIMEZONE" here, finger slippage.
​

> My attempts at working the OP's problem passed through that:
>
> ​​Apologies, I don't have that reply in the thread in my mailbox.
​

> test=> create index docs_birthdate_idx ON docs using btree
> (((meta->>'birthdate')::timestamp));
> ERROR: functions in index expression must be marked IMMUTABLE
>

​ Isn't the point that casting to ::timestamp will still keep the
timezone? Hence casting to "without timezone".

This works:
>
> test=> create index docs_birthdate_idx ON docs using btree
> ((meta->>'birthdate'));
> CREATE INDEX
>
> It is the act of casting that fails. Other then the OP's own suggestion of
> creating
> a function that wraps the operation and marks it immutable I don't have a
> solution at
> this time
>

​I can imagine that without a cast, depending on the way birthdate is
stored, it may behave differently to a cast index for ordering.

Geoff