Jira needs a database driver to connect to your database. By default, these database drivers are included when possible with the Jira installation process.  However due to licensing constraints, some JDBC drivers cannot be bundled with the Atlassian installer packages (such as all MySQL, and some Oracle versions).  The driver is in a file with the '.jar' suffix. The file needs to be copied to the <Jira installation directory>/lib/ directory. Then you need to restart Jira.

The driver file will be different depending on the type of your database and sometimes on the version of the database software you are running.  The supported driver version can also change between version releases of Jira.  Please consult the corresponding Jira Supported platforms documentation for your version of Jira to find the corresponding supported JDBC driver version.