Check what's the CONSTRAINT name and the FOREIGN KEY name:
SHOW CREATE TABLE table_name;
Remove both the CONSTRAINT name and the FOREIGN KEY name:
ALTER TABLE table_name
DROP FOREIGN KEY the_name_after_CONSTRAINT,
DROP KEY the_name_after_FOREIGN_KEY;
Or simply run this if you know the foreign key name:
alter table footable drop foreign key fooconstraint
原文:https://stackoverflow.com/questions/838354/mysql-removing-some-foreign-keys