media-gfx/digikam-5.* and media-gfx/digikam-9999 requires unnecessary USE flag "mysql" on dev-qt/qtsql. digikam[-mysql], built and linked against qtsql[-mysql] is fully operational.
Thanks for the report, this is fixed: https://gitweb.gentoo.org/proj/kde.git/commit/?id=fd702858962c4b44e0611fdcdb2eb3ec371696bd