Re: Functional index adding one

am Thu, dem 03.07.2008, um 11:50:39 +0200 mailte lbarcala(at)freeresearch(dot)org folgendes:
> Hi all:
>
> I'm trying to create a functional index into column position of token
> table (see below). I want to make something like:
>
> CREATE INDEX token_position_func
> ON token (position+1);
>
> but I get:
>
> test=# CREATE INDEX token_position_func
> test-# ON token (position+1);
> ERROR: syntax error at or near "+"
> LINE 2: ON token (position+1);
>
> I read that I can do "ON function(column)" but, is there a built-in
> function in PostgreSQL to do what I want (add one to the value) or have i
> to build one to make this simple calculation?

Right, write your own function for that, for example:

test=# CREATE TABLE token (id int, id_doc int, token text, position int);
CREATE TABLE
test=*# create function get_pos(int) returns int as $$
declare ret int;
begin
select into ret position+1 from token where id=$1;
return ret;
end;
$$language plpgsql immutable;
CREATE FUNCTION
test=*# CREATE INDEX token_position_func ON token (get_pos(position));
CREATE INDEX

Andreas
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Andreas Kretschmer
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