Обсуждение: Problem with function indexing

Hi,

I hate to resort to posting here but I got no responses
in the other groups.  I am following up on an earlier
response on promotion of float4 to float8 in the WHERE
clause.

To get around this, Tom Lockhart suggested that I make a 
function index on float8, but this is what happens:

final99=> create index mx on psc using btree (float8(glat) float8_ops);
ERROR:  internal error: untrusted function not supported.

["psc" is my table and "glat" is a float4].

Any ideas how to do this?  I have successfully made an index
on an externally linked function . . . 

Thanks,

--Martin

===========================================================================

Martin Weinberg                      Phone: (413) 545-3821
Dept. of Physics and Astronomy       FAX:   (413) 545-2117/0648
530 Graduate Research Tower
University of Massachusetts
Amherst, MA  01003-4525

Martin Weinberg <weinberg@osprey.phast.umass.edu> writes:
> final99=> create index mx on psc using btree (float8(glat) float8_ops);
> ERROR:  internal error: untrusted function not supported.

The trouble here is that in 6.4.*, float4-to-float8 is an SQL alias
function, and you can't use an SQL function as the guts of an index.
(I know, the error message is misleading.)

Looking in pg_proc shows that the underlying built-in function is named
"ftod":

play=> select proname,prosrc from pg_proc where proname = 'float8' and
play-> pg_proc.proargtypes[0] = 700;
proname|prosrc
-------+---------------
float8 |select ftod($1)
(1 row)

so if you saycreate index mx on psc using btree (ftod(glat) float8_ops);
it should work.

(BTW, in 6.5 this little fine point goes away, since all the aliases of
a built-in function are equally built-in.)
        regards, tom lane