Drop foreign key only if it exists

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
            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.

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