Re: trying to build immutable function in index

On Tue, Jun 2, 2020 at 2:42 PM Mark Steben <mark(dot)steben(at)drivedominion(dot)com>
wrote:

> Good afternoon,
>
> We are still running postgresql 9.4 - still trying to convince management
> to upgrade :<(
>
> I am trying to create this index (the REGEXP portion is a date check)
>
> create index custattr_value_includes on customer_attributes
> using btree (value, account_id, group_num, id)
> WHERE value::text ~
> '^([0-9][0-9][0-9][0-9])-(([0]?[1-9])|([1][0-2]))-(([0-2]?[0-9])|([3][0-1]))$'::text
>

Regular Expressions provide a nifty construct named "Quantifiers"

https://www.postgresql.org/docs/10/functions-matching.html#FUNCTIONS-POSIX-REGEXP

Predictably the date_trunc portion errors out with this error:
> ERROR: functions in index predicate must be marked IMMUTABLE
> So I copy the source of the 3 flavors of date_trunc as follows:
>
> CREATE OR REPLACE FUNCTION pg_catalog,date_trunc(
> text,
> timestamp with time zone,
> text)
> RETURNS timestamp with time zone
> LANGUAGE 'internal'
>
> COST 1
> STABLE STRICT PARALLEL SAFE
> AS $BODY$timestamptz_trunc_zone$BODY$;
>

That doesn't make any sense.

changing the STABLE behavior to IMMUTABLE
>

I don't see any behavior in the above, changed or otherwise.

and the name from
> pg_catalog.date_trunc to public.my_date_trunc (all three flavors) and
> recompile all three
> Then I change the index source to reference the newly compiled functions
> create index custattr_value_includes on customer_attributes
> using btree (value, account_id, group_num, id)
> WHERE value::text ~
> '^([0-9][0-9][0-9][0-9])-(([0]?[1-9])|([1][0-2]))-(([0-2]?[0-9])|([3][0-1]))$'::text
> AND value::text ~
> '([0-9][0-9][0-9][0-9])-(0[13578]|1[02])-(0[1-9]|[12][0-9]|3[01])|([0-9][0-9][0-9][0-9])-(0[469]|11])-(0[1-9]|[12][0-9]|30)|([0-9][0-9][0248][048]|[0-9][0-9][13579][26])-(02)-(0[1-9]|1[0-9]|2[0-9])|([0-9][0-9][0248][1235679]|[0-9][0-9][13579][01345789])-(02)-(0[1-9]|1[0-9]|2[0-8])'::text
> AND value::date >= my_date_trunc('MONTH'::text, 'now'::text::date - '1
> mon'::interval month)
> AND value::date <= my_date_trunc('DAY'::text, 'now'::text::date::timestamp
> with time zone)
> AND account_id IS NOT NULL
>
> And I am still getting the error: functions in index predicate must be
> marked IMMUTABLE
>
> Am I missing something?
>

A self-contained example. And understanding that even though you place the
"check" regex expression "before" the "value::date" ones there is no
promise of ordering among the various AND clauses. You are trying to
define a static constraint relative to "now" which is a fundamental
violation of what a static constraint does. Time should seldom be a
component of a constraint, variable time should never.

In short, you think what you are doing should work and you think the system
is giving you a bogus error preventing you from doing so. When in fact you
are going about the entire problem incorrectly. If this is really the
general form that you require write a trigger.

David J.