it is no doubt that "select ... where function(slice) > 1 " works but
my question is if the query uses an index on field "slice" and if I
change the function or other parameters of the function if it still uses
that index .
my problem is with text fields . just as an example: in some application
a_text_field is a concatenation of 3 characters for department , 3
character for cost center, other 3 character for location etc ; can i
create o single index on the whole a_text_field (not one for department
, one for cost center etc) , change the function or other parameters of
the function in a "select ... where function(a_text_field,other _param)
= value" and the query still uses the index ?
my question is not about the functionality , that is ok , it is about
the speed/ use of index .
thank you for the answers!!!
Robert Deme wrote:
>
> Hello!!
>
> in flagship ( a variant of clipper for unix , http://www.wgs.com/) it
is
> an interesting statement "seek eval" ; it scans the index and for
every
> position it evaluates a block of code/ function until the function
> return true .
> is in postgresql an internal mechanism or a way to use the index when
> selecting records with conditions like function(index_expression) =
> value ?
I'm not sure I understand the question. There are a large number of
functions built in to PostgreSQL that you can use in your queries. Plus
you can define your own functions in SQL, C, or other languages. If
you're talking about something else, maybe send an example.
DROP TABLE pie;
CREATE TABLE pie (
filling text,
slice float --size in degrees.
);
INSERT INTO pie
VALUES ('blackbird', 90);
INSERT INTO pie
VALUES ('blackbird', 45);
INSERT INTO pie
VALUES ('plum', 120);
SELECT filling, radians( slice ) AS size
FROM pie
WHERE radians( slice ) > 1;
________________________
Ron Peterson
rpeterson@yellowbank.com
