Error: Functions in Index Expression Must Be Marked Immutable in Postgres

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

According to this thread in the hackers mailing list:

http://www.mail-archive.com/pgsql-hackers@postgresql.org/msg86725.html

this is intended behaviour as to_char depends on the LC_MESSAGES setting

In your case this apparently doesn't make sense as the format you are using will never depend on the locale, so if you do need to use the text representation in the index, you can create your own to_char() function and mark it as immutable:

CREATE OR REPLACE FUNCTION my_to_char(some_time timestamp) 
  RETURNS text
AS
$BODY$
    select to_char($1, 'yyyy-mm-dd');
$BODY$
LANGUAGE sql
IMMUTABLE;

If you have to use it as a text in the index (and cannot use the cast to a date as Sam suggested) you will need to create your own formatting function that you can mark as immutable. That can then be used in the index.

But to make Postgres use the index you will need to call my_to_char() in your SQL statements as well. It will not recognize it when you use the built-in to_char()

But I do think Sam's suggestion using a straight date in the index is probably better

Error functions in index expression must be marked IMMUTABLE, not time stamp

You probably want

CREATE INDEX idx_concat_paostartno_paostartsuff
   ON dmv_os_addbase_residential ((pao_start_number || pao_start_suffix));

This index can only be used for queries like

SELECT *
FROM dmv_os_addbase_residential
WHERE pao_start_number || pao_start_suffix <operator> <constant>;

where <operator> is one of =, <, <=, > or >=.

I'm trying to create the following index

time_stamp must be a timestamp with time zone.

You'll have to make the expression IMMUTABLE by converting it to a timestamp without time zone at the appropriate time zone:

CREATE INDEX request_response_partition_idx
ON public.request_response_partition (
   userid,
   extract('Month' FROM (time_stamp AT TIME ZONE 'UTC'))
);

Of course you also have to modify the expression in your queries to match the index.

How do I create an index in PostgreSQL on an expression that uses the date_trunc function?

only date_trunc(text,interval) and date_trunc(text,timestamp) are immutable

create index on test (date_trunc('month', foo::timestamp ));

the problem with foo at time zone 'GMT' is that the expression foo at time zone 'GMT' is not itself immutable. It's not immutable because it depends on the sessions time zone setting.

confusingly at time zone 'GMT' is the inverse of at time zone 'GMT' so if the column being indexed is of type timestamptz (timestamp with timezone) then that operation will fix the index expression.

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