select using an index - Mailing list pgsql-general

Hi

 Recently i created an index in a table using a function (not a column) as following

create index H2IAb on precalc (idr(p1,p4,p6,p7,p9,'H-2*IAb'));,

where idr is a function that returns a real number,

as a result i got the following table

mhc2db=> \d precalc;
                            Table "public.precalc"
 Column |     Type        |                      Modifiers
-------------+-------------------+------------------------------------------------------
 id          | integer         | not null default nextval('precalc_id_seq'::regclass)
 p1         | character(1)  |
 p4         | character(1)  |
 p6         | character(1)  |
 p7         | character(1)  |
 p9         | character(1)  |
Indexes:
    "h2iab" btree (idr(p1, p4, p6, p7, p9, 'H-2*IAb'::character varying)),

now, i would like to perform a query using this index, something like

 
Select * from precalc where h2iab>2

but obviously h2iab  is not a column...

some of you knows what i should do?

thanks

--
Pau Marc Muñoz Torres
Laboratori de Biologia Computacional  
Institut de  Biotecnologia   i Biomedicina Vicent Villar                                    
Universitat Autonoma de Barcelona
E-08193 Bellaterra (Barcelona)
              
telèfon: 93 5812807
Email : paumarc.munoz@bioinf.uab.cat

--
Pau Marc Muñoz Torres

Laboratori de Biologia Computacional  
Institut de  Biotecnologia   i Biomedicina Vicent Villar                                    
Universitat Autonoma de Barcelona
E-08193 Bellaterra (Barcelona)
              
telèfon: 93 5812807
Email : paumarc.munoz@bioinf.uab.cat