This indicates an attack attempt against a Denial of Service vulnerability in MySQL server.
The vulnerability is caused by an error when the vulnerable software handles a malicious SQL request. A remote attacker may be able to exploit this to cause a denial of service condition on an affected server.
MySQL 5.5.19 and possibly other versions
MariaDB 5.5.28a and possibly other versions
Denial of Service: Remote attackers can crash vulnerable systems.
Currently we are unaware of any vendor supplied patch for this issue.