MySQL auto increments disappeared

I have a MySQL database with 60 tables. Most of the tables have primary keys (expect pivot tables). 开发者_JAVA百科All these primary keys had the attribute AUTO INCREMENT.

Then over night somehow all the primary keys had that attribute removed and the default value set to 0.

I have no idea what might have caused this. Any suggestions?

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Improper backup/restore probably. I've recently learned that mysqldump with --skip-opt option will drop auto-increment index :(