Drop foreign key only if it exists

Question

I\'m on a MySQL database.

I\'m doing this, but it doesn\'t work.

ALTER TABLE `object` DROP FOREIGN KEY IF EXISTS `object_ibfk_1`;

I\'ve

Answer 1

If you want to drop foreign key if it exists and do not want to use procedures you can do it this way (for MySQL) :

set @var=if((SELECT true FROM information_schema.TABLE_CONSTRAINTS WHERE
            CONSTRAINT_SCHEMA = DATABASE() AND
            TABLE_NAME        = 'table_name' AND
            CONSTRAINT_NAME   = 'fk_name' AND
            CONSTRAINT_TYPE   = 'FOREIGN KEY') = true,'ALTER TABLE table_name
            drop foreign key fk_name','select 1');

prepare stmt from @var;
execute stmt;
deallocate prepare stmt;

If there is foreign key we put alter table statement in variable and if there isn't we put a dummy statement. And then we execute it.