Re: create index with substr function - Mailing list pgsql-performance

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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