The MYSQL class is the database specification file. An instance of this class is used as generic parameter in EiffelStore. On Windows ---------- You need to have $(MYSQL) in your environment, set to the directory where the MySQL C Connector is installed. (i.e, directory containing the mysql "include" folder). On Linux -------- Either you install libmysqlclient-dev or libmariadb-dev packages For instance on debian: apt install libmysqlclient-dev (or apt install libmariadb-dev) Or, you can also use a custom installation and set in your environment: - $(MYSQLINC) set to the directory where mysql.h is located. - $(MYSQLLIB) set to the directory where libmysqlclient.a is location. For instance, on debian: - To install the needed MySQL packages: apt-get install libmysqlclient-dev (or apt-get install libmariadb-dev) - Note that if mysql_config (or mariadb_config) is not available you should set your environment: export MYSQLINC=/usr/include/mysql export MYSQLLIB=/usr/lib/mysql export MYSQLLIB=/usr/lib/i386-linux-gnu Check your system for the exact locations. Note: If you use an old libmysqlclient (before MySQL 5.5, back at the end of 2009), you may need to edit the .ecf, to use libmysqlclient_r instead of libmysqlclient in multi-threaded applications.