Re: create index with substr function

Tom Lane wrote:

>"Ray" <ray_siu@ge-ts.com.hk> writes:
>  
>
>>CREATE INDEX idx_doc_substr_doc_urn ON doc USING btree (SUBSTR(doc_urn,10));
>>ERROR:  parser: parse error at or near "10" at character 68
>>    
>>
>
>This will work in 7.4, but not older releases.
>
>  
>
Can't you just use a SQL function that calls the substr function? I have 
done that with date functions before
like:

CREATE OR REPLACE FUNCTION get_month(text) returns double precision AS '
   SELECT date_part('month',$1);
' LANGUAGE 'SQL' IMMUTABLE;

CREATE INDEX get_month_idx on foo(get_month(date_field));

Or in this case:

CREATE OR REPLACE FUNCTION sub_text(text) returns text AS '
      SELECT SUBSTR($1,10) from foo;
' LANGUAGE 'SQL' IMMUTABLE;

CREATE INDEX sub_text_idx ON foo(sub_text(doc_urn));

This works on 7.3.6???

Sincerely,

Joshua D. Drake




>			regards, tom lane
>
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