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create index with substr function

From: "Ray" <ray_siu(at)ge-ts(dot)com(dot)hk>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: create index with substr function
Date: 2004-10-21 02:25:17
Message-ID: 069201c4b715$34851670$0f6010ac@raysiu (view raw or flat)
Thread:
Lists: pgsql-performance
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.

Thanks
Ray

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Subject: Re: create index with substr function
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