Re: create index with substr function

From: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>
To: Ray <ray_siu(at)ge-ts(dot)com(dot)hk>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: create index with substr function
Date: 2004-10-21 02:57:54
Message-ID: 20041020195604.T32588@megazone.bigpanda.com
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On Thu, 21 Oct 2004, Ray wrote:

> Hi All,
>
> I have a table in my postgres:
> Table: doc
> Column | Type | Modifiers
> ---------------+-----------------------------+-----------
> doc_id | bigint | not null
> comp_grp_id | bigint | not null
> doc_type | character varying(10)| not null
> doc_urn | character varying(20)| not null
>
> I want to create an index on doc_urn column with using substr function like this:
> CREATE INDEX idx_doc_substr_doc_urn ON doc USING btree (SUBSTR(doc_urn,10));
>
> but there is an error:
>
> ERROR: parser: parse error at or near "10" at character 68
>
> what's wrong for this SQL? As I have found some reference on the
> internet, I can't find anything wrong in this SQL.

What version are you using? If you're using anything previous to 7.4 then
the above definately won't work and the only work around I know of is to
make another function which takes only the column argument and calls
substr with the 10 constant.

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