Install Mysql 5.5 in centos 6.3
As MySQL 5.1 is standard in CentOS/RHEL 6.x, it is not included in the Webtatic EL 6 repository.
Install Atomic Yum Repository On CentOS Linux:
[root@test]# wget -q -O - http://www.atomicorp.com/installers/atomic |sh
then install
yum install mysql55 mysql55-server