Odd numeric->float4/8 casting behaviour
I noticed this odd discrepancy:
postgres=# select -0.999::numeric(3,3)::float4 = -0.999::numeric(3,3);
?column?
----------
f
(1 row)
I believe this is happening because the numeric is being cast to float8 and
then the float4-float8 cross-data-type operator is being used. It seems like
it would be preferable to cast it to float4 and use the non-cross-data-type
operator. They're both marked as implicit casts so I'm unclear what decides
which gets used.
Also, as a side note I was surprised to find the above being parsed as
-(0.999::numeric(3,3)) rather than (-0.999)::numeric(3,3) is that expected?
regression=# create or replace view x as select -0.999::numeric(3,3)::float4 = -0.999::numeric(3,3);
CREATE VIEW
regression=# \d x
View "public.x"
Column | Type | Modifiers
----------+---------+-----------
?column? | boolean |
View definition:
SELECT (- 0.999::numeric(3,3)::real) = (- 0.999::numeric(3,3))::double precision;
regression=# create or replace view x as select (-0.999)::numeric(3,3)::float4 = (-0.999)::numeric(3,3);
CREATE VIEW
regression=# \d x
View "public.x"
Column | Type | Modifiers
----------+---------+-----------
?column? | boolean |
View definition:
SELECT -0.999::numeric(3,3)::real = -0.999::numeric(3,3)::double precision;
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
Gregory Stark <stark@enterprisedb.com> writes:
I believe this is happening because the numeric is being cast to float8 and
then the float4-float8 cross-data-type operator is being used. It seems like
it would be preferable to cast it to float4 and use the non-cross-data-type
operator. They're both marked as implicit casts so I'm unclear what decides
which gets used.
Without having traced through the code, I think the fact that float8 is
a "preferred type" is driving it. It's not clear whether we could
change this without getting into a "can't resolve ambiguous operator"
problem.
Also, as a side note I was surprised to find the above being parsed as
-(0.999::numeric(3,3)) rather than (-0.999)::numeric(3,3) is that expected?
Yeah, :: binds VERY tightly.
regards, tom lane
"Tom Lane" <tgl@sss.pgh.pa.us> writes:
Gregory Stark <stark@enterprisedb.com> writes:
I believe this is happening because the numeric is being cast to float8 and
then the float4-float8 cross-data-type operator is being used. It seems like
it would be preferable to cast it to float4 and use the non-cross-data-type
operator. They're both marked as implicit casts so I'm unclear what decides
which gets used.Without having traced through the code, I think the fact that float8 is
a "preferred type" is driving it. It's not clear whether we could
change this without getting into a "can't resolve ambiguous operator"
problem.
This is pre-operator-families, I thought "preferred type" was new with them.
Perhaps we should have preferred operators rather than preferred types?
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com