Many years ago fREW Schmidt wrote a very handy article on installing MSSQL ODBC drivers in debian. Since then Microsoft have improved their support of debian somewhat and things have changed making it easier to install, however they still (as at 2017-11-06) have not released proper drivers for Debian Stretch.
Add the microsoft repo
echo 'deb [arch=amd64] https://packages.microsoft.com/debian/8/prod jessie main' > /etc/apt/sources.list.d/mssql-release.list
Add the key
curl https://packages.microsoft.com/keys/microsoft.asc | sudo apt-key add -
then update and install
sudo apt update sudo apt install msodbcsql mssql-tools
If you try and connect to sql now you get an obscure error like this:
/opt/mssql-tools/bin/sqlcmd -S 10.0.2.13 -U xxx -P yyy Sqlcmd: Error: Microsoft ODBC Driver 13 for SQL Server : Can't open lib '/opt/microsoft/msodbcsql/lib64/libmsodbcsql-13.1.so.9.1' : file not found.
But the file exists:
$ file /opt/mssql-tools/bin/sqlcmd /opt/mssql-tools/bin/sqlcmd: ELF 64-bit LSB executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=21a353af470e7849544daab892ec9b1bfc36dc87, not stripped
This somewhat misleading error is actually due to the libmsodbcsql lib being linked against a very specific version of libssl. Check the output of ldd:
$ ldd /opt/microsoft/msodbcsql/lib64/libmsodbcsql-13.1.so.9.1 | grep 'not found' libcrypto.so.1.0.0 => not found libssl.so.1.0.0 => not found
But it turns out this can easily be solved by manually installing the libssl package from Debian Jessie:
wget http://security.debian.org/debian-security/pool/updates/main/o/openssl/libssl1.0.0_1.0.1t-1+deb8u7_amd64.deb sudo apt install ./libssl1.0.0_1.0.1t-1+deb8u7_amd64.deb
then you should be back in business.