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

Instead of using to_char to format your timestamp as YYYY-MM-DD, try casting your timestamp to a date type, which will have the same effect:

create index CONCURRENTLY idx_test on  tmp_table using btree (skyid, cast(create_time as date), actiontype );