How to install MySQL-server-5.5 on ubuntu 16.04:
I have tried :
sudo apt-get install mysql-server-5.5
but, E: Package 'mysql-server-5.5' has no installation candidate.
How can i solve it..?
MySQL 5.5 is not officially available for Ubuntu 16.04, neither from the Ubuntu developers (the only available version is 5.7) nor from the MySQL ones (only 5.6, 5.7, and the in-development 8.0).
It is available unofficially from this PPA, so if you really need 5.5, that's probably your best bet. However, you should really install from an official source if at all possible; this would mean either installing MySQL 5.6+ on 16.04, or installing 14.04, which has MySQL 5.5 in its official Ubuntu repositories.
Install MySQL 5.5
Use the following commands to install MySQL 5.5 on your Ubuntu 16.04 and 15.10 systems. If it is not specifically required, we recommend to use higher version of MySQL than 5.5.
$ sudo apt-get install software-properties-common
$ sudo add-apt-repository -y ppa:ondrej/mysql-5.5
$ sudo apt-get update
$ sudo apt-get install mysql-server-core-5.5