Drop muli-column unique key without dropping foreign key?

Question

I am trying to delete a multi-column unique key from a table that also has a foreign key. I keep getting \'errno 150\', unless I delete the foreign key first.

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Answer 1

a FOREIGN KEY REFERENCES, require a key,
the only key that can be used is t_unique_key, thats why you can't remove it.
so add another matching key first, and then remove the old key, in your case the othertable_id field

ALTER TABLE `testtable`
ADD KEY (othertable_id),
DROP KEY `tt_unique_key`;