[#MDEV-26646] SFORMAT Does not allow @variable use

[MDEV-26646] SFORMAT Does not allow @variable use Created: 2021-09-20 Updated: 2021-10-12 Resolved: 2021-10-12
Status:	Closed
Project:	MariaDB Server
Component/s:	Character Sets, Server
Affects Version/s:	10.7
Fix Version/s:	10.7.1

Type:

Bug

Priority:

Critical

Reporter:

Roel Van de Paar

Assignee:

Sergei Golubchik

Resolution:

Fixed

Votes:

0

Labels:

None

Issue Links:

Problem/Incident
is caused by	~~MDEV-25015~~	Custom formatting of strings in Maria...	Closed

Description

10.7.0 53b2c1f4664a3cb90f583979d9aa2771b7e1c98d (Debug) preview-10.7-MDEV-25015-sformat
10.7.0-dbg>SET @a=3.14;
Query OK, 0 rows affected (0.000 sec)

10.7.0-dbg>CREATE TABLE t1 SELECT @a;
Query OK, 1 row affected (0.019 sec)
Records: 1 Duplicates: 0 Warnings: 0

10.7.0-dbg>SHOW CREATE TABLE t1\G
************************* 1. row *************************
Table: t1
Create Table: CREATE TABLE `t1` (
`@a` decimal(65,38) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.000 sec)

10.7.0-dbg>SELECT SFORMAT ('FLOAT {:.5f}',@a);
+-----------------------------+
\| SFORMAT ('FLOAT {:.5f}',@a) \|
+-----------------------------+
\| NULL \|
+-----------------------------+
1 row in set, 1 warning (0.000 sec)

10.7.0-dbg>SHOW WARNINGS;
+---------+------+---------------------------------------+
\| Level \| Code \| Message \|
+---------+------+---------------------------------------+
\| Warning \| 4183 \| SFORMAT error: invalid type specifier \|
+---------+------+---------------------------------------+
1 row in set (0.000 sec)

10.7.0-dbg>SELECT SFORMAT ('FLOAT {:.5f}',3.14);
+-------------------------------+
\| SFORMAT ('FLOAT {:.5f}',3.14) \|
+-------------------------------+
\| FLOAT 3.14000 \|
+-------------------------------+
1 row in set (0.000 sec)

Comments

Comment by Sergei Golubchik [ 2021-10-09 ]

please, take a look at the commit

commit e800625d80c

Author: Sergei Golubchik <serg@mariadb.org>

Date:   Sat Oct 9 16:00:13 2021 +0200

    MDEV-26646 SFORMAT Does not allow @variable use

    If charset aggregation decides to convert arguments to some specific

    charset and some arguments are numbers, they'll be wrapped into a

    Item_func_conv_charset(), that changes result_type() to STRING_RESULT.

    Fix: don't convert numbers, sformat needs their numerical value only.

I'm particularly interested in alternative approaches, e.g. pass a flag MY_COLL_SKIP_NUMBERS. Or just always skip numbers everywhere unconditionally.

Comment by Alexander Barkov [ 2021-10-12 ]

We cannot always skip numbers unconditionally inside all Item_func_xxx. The following examples won't work:

CONCAT(ucs2arg,1)

SET collation_connection=ucs2_general_ci;

SELECT CONCAT(1);

SELECT LEFT(123,1);

I think your patch is good.

Alternatively, we could try to do the following for Item_func_sformat:

Don't call Type_std_attributes::agg_item_set_converter() in fix_length_and_dec().
This won't wrap arguments into Item_func_conv_charset.
Instead, perform the conversion using this method for the string arguments:

/*

    Returns the val_str() value converted to the given character set.

*/

  String *val_str(String *str, String *converter, CHARSET_INFO *to);

However, there will be a difference comparing to other functions, e.g. CONCAT():
1. It won't return "Illegal mix of collations" for potentially lossy charset combinations during fix_fields().
It will just replace non-convertable characters to question marks during val_str() without warnings.
2. Item_func_conv_charset implements some caching functionality for constant expressions.
Caching will disappear.

I'm slightly inclined to your solution for now.

Comment by Sergei Golubchik [ 2021-10-12 ]

pushed into a preview branch

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