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List:       postgresql-sql
Subject:    Re: [SQL] creating an index on a function
From:       Brent Verner <brent () rcfile ! org>
Date:       2002-02-15 15:42:52
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[2002-02-15 09:26] Nick Fankhauser said:
| Good Morning everyone!
| 
| I just tried to create an index on a function with no success. My syntax
| seems to match the syntax shown in the docs for Create Index, but I get an
| error. Any thoughts would be appreciated. Here is my attempt-
| 
| First, I did a select to make sure I had the function syntax correct, and
| then tried to create the index:
| 
| 
| staging=# select count(*) from event where
| date_trunc('day',event_date_time)='07/27/2001';
|  count
| -------
|     27
| (1 row)
| 
| staging=#
| staging=# create index event_day on
| event(date_trunc('day',event_date_time));

You cannot create an index on a function with constant parameters.
This limitation may be removed in a future version, but for now
you have to create a wrapper function that doesn't require the
constant parameter

  CREATE FUNCTION date_trunc_day(TIMESTAMP) RETURNS TIMESTAMP AS '
     SELECT date_trunc(''day'',$1);
  ' LANGUAGE 'sql';

then use this to create your function index.
  
   create index event_day on
     event(date_trunc_day(event_date_time));

hth.
  brent

-- 
"Develop your talent, man, and leave the world something. Records are 
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