creating index with a cast statement in the predicate

[Mark Steben <mark.steben@xxxxxxxxxxxxxxxxx>]

Good afternoon

I am currently running postgres 9.4.8.

    I would like to create an index on a column named value: defined as varchar(255)

Values in this column can be many, including both dates and non-dates.

The developers run a query that first uses a regular _expression_ to filter non-dates out

then, ANDS it with the following  

 and cast(value as date) >= date_trunc('MONTH', current_date) - interval ' 2 Month '

    When I attempt to create an index using this statement in the predicate, I get the error that states that functions in an index predicate must be marked as Immutable.

Our internal functions date_trunc (all 3) and date are all already defined as immutable.

I can create an index with the regular _expression_ as the predicate but not the cast statement comparison.

   Here is the regular _expression_ index I constructed:

  "primets_custattr_small_regexp" btree (value) WHERE value::text ~ '([0-9][0-9][0-9][0-9])-(0[13578]|1[02])-(0[1-9]|[12][0-9]|3[01])|([0-9][0-9][0-9][0-9])-(0[469]|11])-(0[1-9]|[12][0-9]|30)|([0-9][0-9][0248][048]|[0-9][0-9][13579][26])-(02)-(0[1-9]|1[0-9]|2[0-9])|([0-9][0-9][0248][1235679]|[0-9][0-9][13579][01345789])-(02)-(0[1-9]|1[0-9]|2[0-8])'::text

I would appreciate any insight here.  Thank you

 

--

Mark Steben
 Database Administrator
@utoRevenue | Autobase 
  CRM division of Dominion Dealer Solutions 
95D Ashley Ave.
West Springfield, MA 01089
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f: 413.383-9567

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