Re: patch (for 9.1) string functions

2010/7/13 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:
> so this is actualised patch:
> * concat_sql removed
> * left, right, reverse and concat are in core
> * printf and concat_ws are in contrib
> * format show "<NULL>" as NULL string
> * removed an using of wide chars

I think function codes in the core (concat, format, left, right,
and reverse) are ready for committers. They also have docs, but
the names are not listed in Index page (bookindex.html).
Please add
<indexterm>
<primary>funcname</primary>
</indexterm>
in func.sgml for each new function.

However, I have a couple of comments to stringfunc module. sprintf()
and concat_ws() are not installed by default, but provided by the module.

> todo:
> NULL handling for printf function

I like <NULL> for null arguments. It is just same as format() and RAISE.

=== Questions ===
* concat_ws() transforms NULLs into empty strings.
Is it an intended behavior and compatible with MySQL?
Note that string_agg() doesn't add separators to NULLs.

=# SELECT coalesce(concat_ws(',', 'A', NULL, 'B'), '(null)');
coalesce
----------
A,,B
(1 row)

* concat_ws() returns NULL when the separator is NULL.
Is it an intended behavior and compatible with MySQL?

=# SELECT coalesce(concat_ws(NULL, 'A', NULL, 'B'), '(null)');
coalesce
----------
(null)
(1 row)

=== Trivial issues ===
* Some function prototypes are declared but not used.
We can just remove them.
- mb_string_info()
- stringfunc_concat(PG_FUNCTION_ARGS);
- stringfunc_left(PG_FUNCTION_ARGS);
- stringfunc_right(PG_FUNCTION_ARGS);
- stringfunc_reverse(PG_FUNCTION_ARGS);

* Some error messages need to be improved.
For example, "1th" is wrong.
=# select sprintf('>>>%*s<<<', NULL, 'abcdef');
ERROR: null value not allowed
HINT: width (1th) arguments is NULL

* sprintf() has some typos in error messages
For example, "sprinf".

--
Itagaki Takahiro