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

Question

I want to create a Multicolumn expression index, but when I create the index, the following message is output:

--detail message 
wapgrowth=> create index          


        

Answer 1

to_char of a timestamp-without-timezone is not an immutable function, because the conversion depends on your local time-zone setting. That means the index wouldn't be portable to another computer in a different time zone, and Postgres won't allow it. I think the problem will go away if you declare create_time as a time with timezone.