Hello. I found that 9.5 has an undocumented difference from 9.4
in type cast in pl/pgsql and I think it might better be mentioned
as a change of behavior in release notes.
Whether do you think it is worth mentioning or not in release notes?
=====
9.4 and 9.5 has difference in casting between floating point
numbers.
CREATE OR REPLACE FUNCTION hoge () RETURNS text AS $$ DECLARE vr real; vf8
float8; BEGIN vr := 0.1; vf8 = vr; RETURN 'hoge = '|| vf8 ; END; $$ LANGUAGE
plpgsql;
9.5=# select hoge();
hoge
--------------------------
hoge = 0.100000001490116
9.4=# select hoge();
hoge
------------
hoge = 0.1
This is stemming from the difference between '0.1'::real::float8
and '0.1'::real::text::float8, made in exec_cast_value().
=# select '0.1'::real::float8, '0.1'::real::text::float8;
float8 | float8
-------------------+--------
0.100000001490116 | 0.1
This example itself looks somewhat artifitial but it would be
rather common to load real values in a table into float8
variables in a function for further calculations.
This is a side effect of the commit
1345cc67bbb014209714af32b5681b1e11eaf964 and the relase notes has
the following discription corresponds to this commit in the
Migration section, with no mention of this.
> Use assignment cast behavior for data type conversions in
> PL/pgSQL assignments, rather than converting to and from text
> (Tom Lane)
>
> This change causes conversions of Booleans to strings to produce
> true or false, not t or f. Other type conversions may succeed in
> more cases than before; for example, assigning a numeric value
> 3.9 to an integer variable will now assign 4 rather than
> failing. If no assignment-grade cast is defined for the
> particular source and destination types, PL/pgSQL will fall back
> to its old I/O conversion behavior.
Whether do you think it is worth mentioning or not?
Though the attached patch adds a description for that, it should
be rewritten even if this is worth mentioning.
+ This change also may bring different results of type casts
+ between floating point numbers having different conversion
+ errors.
regards,
--
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/doc/src/sgml/release-9.5.sgml b/doc/src/sgml/release-9.5.sgml
index 64057c3..5c86222 100644
--- a/doc/src/sgml/release-9.5.sgml
+++ b/doc/src/sgml/release-9.5.sgml
@@ -108,7 +108,9 @@
an integer variable will now assign 4 rather than failing. If no
assignment-grade cast is defined for the particular source and
destination types, <application>PL/pgSQL</> will fall back to its old
- I/O conversion behavior.
+ I/O conversion behavior. This change also may bring different results of
+ type casts between floating point numbers having different conversion
+ errors.
</para>
</listitem>
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