Starting with MySQL 8.0.16, you can finally substract privileges, although for now, only from global grants (e.g. you cannot yet do it for individual columns), but it is worth noting:
As of MySQL 8.0.16, it is possible to explicitly deny a privilege granted at the global level by revoking it for particular databases, if the partial_revokes system variable is enabled:
GRANT SELECT, INSERT, UPDATE ON *.* TO u1;
REVOKE INSERT, UPDATE ON db1.* FROM u1;
The partial_revokes
system variable has to be set for this:
Enabling this variable makes it possible to revoke privileges partially. Specifically, for users who have privileges at the global level, partial_revokes enables privileges for specific schemas to be revoked while leaving the privileges in place for other schemas. For example, a user who has the global UPDATE privilege can be restricted from exercising this privilege on the mysql system schema. (Or, stated another way, the user is enabled to exercise the UPDATE privilege on all schemas except the mysql schema.) In this sense, the user's global UPDATE privilege is partially revoked.