ruby on rails - Scoped AUTO_INCREMENT in MySQL? -

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i using mysql in rails application. have users table (standard stuff id, name etc) , books table (again id, user_id , title etc).

i have column (lets call user_book_id) should auto incremented id scoped user_id. id, if record deleted in books table, user_book_id should not reused. example:

user  id | name ------------ 1  | jerry 2  | newman  book  id | user_id | user_book_id | title ----------------------------------- 1  | 1       | 1            | jerry's first book 2  | 1       | 2            | jerry's second book 3  | 2       | 1            | newman's first book 4  | 1       | 3            | jerry's third book

is there way in mysql? searched not find anything.

thanks, prateek

no, no such thing exists. either allow auto_increment unique across table, or have implement yourself.


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