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

Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> writes:
> On 02/26/2017 08:50 AM, Tom Lane wrote:
>> I'm not entirely sure why the OP feels he needs an index on this
>> expression. If he's willing to restrict the column to have the
>> exact format 'YYYY-MM-DD', then a regular textual index would sort
>> the same anyway. Perhaps what's needed is just to add a CHECK
>> constraint verifying that the column has that format.

> The OP is trying to create an index on the value of a jsonb key. Would
> the above still apply or am I misunderstanding the reference to column?

Sure, I was using "column" loosely to refer to the meta->>'birthdate'
expression.

> The below works:
> test=> create index docs_birthdate_idx ON docs using btree
> ((meta->>'birthdate'));
> CREATE INDEX
> So if the text values of 'birthdate' are consistent the index would work
> without the cast?

Yeah, seems to me you could do things like
... WHERE meta->>'birthdate' > '2017-02-26'
and it would Just Work, though I'd admit there's a deficiency of sanity
checking for the RHS constant in this example.

regards, tom lane