MySQL Bugs: #25221: Character set of string constant is ignored

Bug #25221	Character set of string constant is ignored
Submitted:	20 Dec 2006 18:23	Modified:	11 Jul 2007 19:52
Reporter:	Alexander Nozdrin	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Stored Routines	Severity:	S3 (Non-critical)
Version:	5.0	OS:	Any
Assigned to:	Alexander Nozdrin	CPU Architecture:	Any
Tags:	rt_q1_2007

Description:
Character set and collation of string literals used in triggers
should be fixed at compilation time. Now they depend
on actual character set / collation of user connection.

See also BUG#25212 (the same problem for stored routines).

How to repeat:
1. Set connection character set to UTF8; create a trigger, that contains string literal and inserts its character set into a "log table";

2. Change connection character set to KOI8-R;

3. Activate the trigger (during the first activation, the trigger will be compiled);

4. Change connection character set to CP1251;

5. Flush trigger cache (rename or alter table);

6. Activate the trigger (the trigger will be compiled again);

7. Analyze results of the "log table" -- character sets will be different from UTF8.

--------------------------------------------------------------

mysql> create table t1(a int, b varchar(32));
Query OK, 0 rows affected (0.03 sec)

mysql> set names utf8;
Query OK, 0 rows affected (0.01 sec)

mysql> create trigger t1_bi before insert on t1 for each row set new.b = charset('a');
Query OK, 0 rows affected (0.01 sec)

mysql> set names koi8r;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t1 values(1, 'xxx');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t1;
+------+-------+
| a    | b     |
+------+-------+
|    1 | koi8r |
+------+-------+
1 row in set (0.00 sec)

mysql> set names cp1251;
Query OK, 0 rows affected (0.01 sec)

mysql> alter table t1 add column fake int;
Query OK, 1 row affected (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> alter table t1 drop column fake;
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into t1 values(2, 'xxx');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t1;
+------+--------+
| a    | b      |
+------+--------+
|    1 | koi8r  |
|    2 | cp1251 |
+------+--------+
2 rows in set (0.00 sec)

Queued into 5.1-runtime

Actually also was reviewed by Alexander Barkov

Final changeset:

ChangeSet
anozdrin/alik@ibm.|ChangeSet|20070628173454|18968 2007/06/28 21:34:54+04:00 anozdrin@ibm. +82 -0
Patch for the following bugs:
- BUG#11986: Stored routines and triggers can fail if the code
has a non-ascii symbol
- BUG#16291: mysqldump corrupts string-constants with non-ascii-chars
- BUG#19443: INFORMATION_SCHEMA does not support charsets properly
- BUG#21249: Character set of SP-var can be ignored
- BUG#25212: Character set of string constant is ignored (stored routines)
- BUG#25221: Character set of string constant is ignored (triggers)

There were a few general problems that caused these bugs:
1. Character set information of the original (definition) query for views,
triggers, stored routines and events was lost.
2. mysqldump output query in client character set, which can be
inappropriate to encode definition-query.
3. INFORMATION_SCHEMA used strings with mixed encodings to display object
definition;

1. No query-definition-character set.

In order to compile query into execution code, some extra data (such as
environment variables or the database character set) is used. The problem
here was that this context was not preserved. So, on the next load it can
differ from the original one, thus the result will be different.

The context contains the following data:
- client character set;
- connection collation (character set and collation);
- collation of the owner database;

The fix is to store this context and use it each time we parse (compile)
and execute the object (stored routine, trigger, ...).

2. Wrong mysqldump-output.

The original query can contain several encodings (by means of character set
introducers). The problem here was that we tried to convert original query
to the mysqldump-client character set.

Moreover, we stored queries in different character sets for different
objects (views, for one, used UTF8, triggers used original character set).

The solution is
- to store definition queries in the original character set;
- to change SHOW CREATE statement to output definition query in the
binary character set (i.e. without any conversion);
- introduce SHOW CREATE TRIGGER statement;
- to dump special statements to switch the context to the original one
before dumping and restore it afterwards.

Note, in order to preserve the database collation at the creation time,
additional ALTER DATABASE might be used (to temporary switch the database
collation back to the original value). In this case, ALTER DATABASE
privilege will be required. This is a backward-incompatible change.

3. INFORMATION_SCHEMA showed non-UTF8 strings

The fix is to generate UTF8-query during the parsing, store it in the object
and show it in the INFORMATION_SCHEMA.

Basically, the idea is to create a copy of the original query convert it to
UTF8. Character set introducers are removed and all text literals are
converted to UTF8.

This UTF8 query is intended to provide user-readable output. It must not be
used to recreate the object. Specialized SHOW CREATE statements should be
used for this.

The reason for this limitation is the following: the original query can
contain symbols from several character sets (by means of character set
introducers).

Example:

- original query:
CREATE VIEW v1 AS SELECT _cp1251 'Hello' AS c1;

- UTF8 query (for INFORMATION_SCHEMA):
CREATE VIEW v1 AS SELECT 'Hello' AS c1;

Pushed into 5.1.21-beta

Noted in 5.1.21 changelog.

(Description applies to Bug#11986, Bug#16291, Bug#19443,
Bug#21249, Bug#25212, Bug#25221)

Several issues were identified for stored programs
containing non-ASCII symbols. These issues involved
conversion errors due to incomplete character set
information when translating these objects to and from
stored format, such as:

* Parsing the original object definition so that it
  can be stored.

* Compiling the stored definition into executable form
  when the object is invoked.

* Retrieval of object definitions from 
  INFORMATION_SCHEMA tables.

* Displaying the object definition in SHOW statements.
  This issue also affected mysqldump, which uses SHOW.

The fix for the problems is to store character set
information from the object creation context so that this
information is available when the object needs to be used
later. The context includes the client character set, the
connection character set and collation, and the collation
of the database with which the object is associated.
As a result of the patch, several tables have new
columns:

* In the mysql database, the proc and event tables now
  have these columns: character_set_client, 
  collation_connection, db_collation, body_utf8.

* In INFORMATION_SCHEMA, the VIEWS table now has these
  columns: CHARACTER_SET_CLIENT, COLLATION_CONNECTION.
  The ROUTINES, TRIGGERS, and EVENT tables now have
  these columns: CHARACTER_SET_CLIENT,
  COLLATION_CONNECTION, DATABASE_COLLATION.

These columns store the session values of the
character_set_client and collation_connection system
variables, and the collation of the database with which
the object is associated. The values are those in effect
at object creation time. (The saved database collation is
not the value of the collation_database system variable,
which applies to the default database; the database that
contains the object is not necessarily the default
database.)

Several SHOW statements now display additional columns
corresponding to the new table columns. These statements
are: SHOW CREATE EVENT, SHOW CREATE FUNCTION, SHOW CREATE
PROCEDURE, SHOW CREATE VIEW, SHOW EVENTS, SHOW FUNCTION
STATUS, SHOW PROCEDURE STATUS, SHOW TRIGGERS.