Clean 'type' and make it an ENUM > select distinct type from systempreferences; +-------------------+ | type | +-------------------+ | textarea | | Free | | YesNo | | Choice | | Integer | | | | multiple | | ill-backends | | ClassSources | | NULL | | File | | multiple_sortable | | Themes | | Languages | | Short | +-------------------+ NULL, File, Short and empty string are not valid types.