Download mssql from the microsoft website.
wget https://packages.microsoft.com/ubuntu/16.04/mssql-server/pool/main/m/mssql-server/mssql-server_14.0.1.246-6_amd64.deb
dpkg -i mssql-server_14.0.1.246-6_amd64.deb
The next command will install dependancies.
sudo apt-get -f install
You will find that you need to upgrade openssl to a version that is not in jessie.
Use jessie backports to upgrade openssl.
nano /etc/apt/sources.list
deb http://debian.uchicago.edu/debian/ jessie-backports main contrib non-free
deb-src http://debian.uchicago.edu/debian/ jessie-backports main contrib non-free
Replace debian.uchicago.edu with your nearest debian repository.
sudo apt-get -t jessie-backports upgrade openssl
sudo apt-get -f install
Then
sudo /opt/mssql/bin/sqlservr-setup