I want to update mysql vertion 5.5.59 to 5.7.21 I'm trying to update my mysql version but it showing error I'm using Linux mint 17.3 version 

used command

sudo apt-get install mysql-server mysql-client mysql-common mysql-server-core-5.7 mysql-client-core-5.7

it showing this

  Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package mysql-client-core-5.7 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  mysql-cluster-community-client:i386 libmysqlclient-dev:i386
  mysql-community-client:i386 mysql-cluster-community-client
  libmysqlclient-dev mysql-community-client

Package mysql-server-core-5.7 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  mysql-common:i386 mysql-cluster-community-server:i386
  mysql-community-server:i386 mysql-common mysql-cluster-community-server
  mysql-community-server

E: Package 'mysql-server-core-5.7' has no installation candidate
E: Package 'mysql-client-core-5.7' has no installation candidate



  mysql -v


mysql  Ver 14.14 Distrib 5.5.59, for debian-linux-gnu (x86_64) using readline 6.3


how can i fix this??
First, never try to uninstall or purge your mysql packages. Your db be drop from your system for ever…

Secondly, you should try to use apt-cache policy mysql* to check which versions are available on your system.

Thirdly, you should do a backup of ALL you DB.

If it is a simple update, you should try sudo apt-get upgrade mysql-client mysql-server mysql-common.

Or more aggressive sudo apt-get dist-upgrade mysql-client mysql-server mysql-common

If not, use the version available for update from apt-cache policy mysql* output.

And, from what I can see, your source.list seems not to contain any repo that contains mysql-server-core-5.7. So use apt-cache policy mysql*.