cast not IMMUTABLE? - Mailing list pgsql-admin

From Gaetano Mendola
Subject cast not IMMUTABLE?
Date
Msg-id c7ei84$j0e$1@floppy.pyrenet.fr
Whole thread Raw
Responses Re: cast not IMMUTABLE?  (Sam Barnett-Cormack <s.barnett-cormack@lancaster.ac.uk>)
Re: cast not IMMUTABLE?  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: cast not IMMUTABLE?  (Stephan Szabo <sszabo@megazone.bigpanda.com>)
List pgsql-admin
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











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