MySQL Bugs: #10409: ON UPDATE CASCADE does not enforce maximum length of UTF-8 data

Bug #10409	ON UPDATE CASCADE does not enforce maximum length of UTF-8 data
Submitted:	6 May 2005 11:47	Modified:	4 Jul 2005 10:17
Reporter:	Marko Mäkelä	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: InnoDB storage engine	Severity:	S3 (Non-critical)
Version:	5.0.6-bk	OS:	Any (all)
Assigned to:	Marko Mäkelä	CPU Architecture:	Any

Description:
The part of InnoDB that implements ON UPDATE CASCADE in 5.0 checks the maximum length of UTF-8 columns in terms of bytes, not characters. Thus, for ROW_FORMAT=COMPACT tables, it may write longer strings than those that can be written by INSERT or UPDATE.

How to repeat:
create table parent(a char(5) primary key) engine=innodb charset=utf8;
create table child(a varchar(4) primary key,constraint c foreign key(a)references parent(a) on update cascade) engine=innodb charset=utf8;

insert into parent values ('abc'),('def'),('gh');
insert into child values ('abc'),('def');
update parent set a='bcdef' where a='def';

-- the child table will incorrectly be updated to 'bcdef'

Suggested fix:
Check the updated length of the column in characters rather than bytes when a variable-length character set (such as UTF-8) is being used.

Marko,

please look at this.

--Heikki

This bug was closed in 5.0.8 in the same changeset with Bug #10511, if I remember correctly. Only the status of Bug #10511 was updated automatically. I'm sorry for not checking this manually.