If you would like to use a MySQL database for several Kodi clients that use different methods to access the shared media (e.g. a mix of SMB, NFS and/or system mount based access), or have need of modifying a path of an existing source (such as converting from a Kodi path to a system mount) you can use the path substitution function of Kodi to facilitate this. The following guide will provide instruction on how this works, including a section specific to MySQL usage and how your sources should be configured.
Please see [HowTo] Repairing File Paths with Path Substitution for details.