/usr/lib/x86_64-linux-gnu/libmysqlcppconn.a is in libmysqlcppconn-dev 1.1.7-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libmysqlcppconn-static.a
/usr/lib/x86_64-linux-gnu/libmysqlcppconn-static.a