cast not IMMUTABLE?

[Gaetano Mendola]

Hi all,
I have a table with ~ 3e+6 rows on it.

I do select on this table in this way:


(1) select * from user_logs where login_time::date = now()::date;


consider that login_time is a TIMESTAMPTZ with an index on it.

If I use the select in this way:

select * from user_logs where login_time = now();

the the index is used.

I'm trying to use define and index in order to help the query (1):


test# create index idx on user_logs ( (login_time::date) );
ERROR: functions in index expression must be marked IMMUTABLE


why that cast is not considered IMMUTABLE ?


How can I define an index for the query (1) ?


Regards
Gaetano Mendola

[Sam Barnett-Cormack]

Post by Gaetano Mendola
Hi all,
I have a table with ~ 3e+6 rows on it.
(1) select * from user_logs where login_time::date = now()::date;
consider that login_time is a TIMESTAMPTZ with an index on it.
select * from user_logs where login_time = now();
the the index is used.
test# create index idx on user_logs ( (login_time::date) );
ERROR: functions in index expression must be marked IMMUTABLE
why that cast is not considered IMMUTABLE ?
How can I define an index for the query (1) ?

The way I have done such queries hs been to create functions, marked
immutable, that encapsulate the cast/non-immutable internal function, if
I know that it *is* really immutable, at least for my purposes, and use
a functional index.

[Stephan Szabo]

Post by Gaetano Mendola
Hi all,
I have a table with ~ 3e+6 rows on it.
(1) select * from user_logs where login_time::date = now()::date;
consider that login_time is a TIMESTAMPTZ with an index on it.
select * from user_logs where login_time = now();
the the index is used.
test# create index idx on user_logs ( (login_time::date) );
ERROR: functions in index expression must be marked IMMUTABLE
why that cast is not considered IMMUTABLE ?

I'd think the conversion of a timestamptz -> date would be dependent on
timezone which would make it not immutable.


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