When migrating the DB from sqlite to mysql does not work (Beim Erstellen der Tabellen in der Datenbank ist ein Fehler aufgetreten.” or ) , edit the edit the /usr/share/kde4/apps/digikam/database/dbconfig.xml configuration file as root and

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<                             UNIQUE(albumRoot, relativePath(255)));</statement>
---
>                             UNIQUE(albumRoot, relativePath(332)));</statement>
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<                             UNIQUE (album, name(255)));</statement>
---
>                             UNIQUE (album, name(332)));</statement>
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<                             UNIQUE (imageid, property(255)));</statement>
---
>                             UNIQUE (imageid, property(332)));</statement>
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<                             UNIQUE(keyword(255)));</statement></dbaction>
---
>                             UNIQUE(keyword(333)));</statement></dbaction>                                                                                   
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<                             UNIQUE(path(254)))
---
>                             UNIQUE(path(333)))
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<                             UNIQUE(keyword(254)))
---
>                             UNIQUE(keyword(333)))

found this by

export MYSQL D_ DEBUG=yes
/etc / init.d / mysql restart
and 
checking the mysqld-query.log  log 

(which then did not work because the permissions were wrong for the mysql log folder until I fixed them.)