How to remove constraints from my MySQL table? - mysql

Question

I want to remove constraints from my table. My query is:
ALTER TABLE `tbl_magazine_issue`
DROP CONSTRAINT `FK_tbl_magazine_issue_mst_users`
But I got an error:
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'constraint FK_tbl_magazine_issue_mst_users' at line 1

Answer 1

Mysql has a special syntax for dropping foreign key constraints:
ALTER TABLE tbl_magazine_issue
DROP FOREIGN KEY FK_tbl_magazine_issue_mst_users

Answer 2

I had the same problem and I got to solve with this code:
ALTER TABLE `table_name` DROP FOREIGN KEY `id_name_fk`;
ALTER TABLE `table_name` DROP INDEX `id_name_fk`;

Answer 3

There is no such thing as DROP CONSTRAINT in MySQL. In your case you could use DROP FOREIGN KEY instead.

Answer 4

If the constraint is not a foreign key, eg. one added using 'UNIQUE CONSTRAINT (colA, colB)' then it is an index that can be dropped using ALTER TABLE ... DROP INDEX ...

Answer 5

To add a little to Robert Knight's answer, since the title of the post itself doesn't mention foreign keys (and since his doesn't have complete code samples and since SO's comment code blocks don't show as well as the answers' code blocks), I'll add this for unique constraints. Either of these work to drop the constraint:
ALTER TABLE `table_name` DROP KEY `uc_name`;
or
ALTER TABLE `table_name` DROP INDEX `uc_name`;

Answer 6

Also nice, you can temporarily disable all foreign key checks from a mysql database:
SET FOREIGN_KEY_CHECKS=0;
And to enable it again:
SET FOREIGN_KEY_CHECKS=1;

Answer 7

Some ORM's or frameworks use a different naming convention for foreign keys than the default FK_[parent table]_[referenced table]_[referencing field], because they can be altered.
Laravel for example uses [parent table]_[referencing field]_foreign as naming convention. You can show the names of the foreign keys by using this query, as shown here:
SELECT CONSTRAINT_NAME FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE REFERENCED_TABLE_SCHEMA = '<database>' AND REFERENCED_TABLE_NAME = '<table>';
Then remove the foreign key by running the before mentioned DROP FOREIGN KEY query and its proper name.

Answer 8

The simplest way to remove constraint is to use syntax ALTER TABLE tbl_name DROP CONSTRAINT symbol; introduced in MySQL 8.0.19:
As of MySQL 8.0.19, ALTER TABLE permits more general (and SQL standard) syntax for dropping and altering existing constraints of any type, where the constraint type is determined from the constraint name
ALTER TABLE tbl_magazine_issue DROP CONSTRAINT FK_tbl_magazine_issue_mst_users;
db<>fiddle demo

Answer 9

For those that come here using MariaDB:
Note that MariaDB allows DROP CONSTRAINT statements in general, for example for dropping check constraints:
ALTER TABLE table_name
DROP CONSTRAINT constraint_name;
https://mariadb.com/kb/en/library/alter-table/

Answer 10

Go to structure view of the table
You will see 2 option at top a.Table structure b.Relation view.
Now click on Relation view , here you can drop your foreign key constraint. You will get all relation here.

Answer 11

In MySQL you have to specify what kind of constraint you want to remove:
Example:
CONSTRAINT `shop_ibfk_1` FOREIGN KEY (`fb_user_id`) REFERENCES `fb_user` (`id`),
CONSTRAINT `shop_chk_1` CHECK ((`import_lock` in (0,1)))
the first one you would remove with:
alter mytable shop drop FOREIGN KEY `shop_ibfk_1`;
the second one with
alter mytable drop CHECK `shop_chk_1`;

Answer 12

this will works on MySQL to drop constraints
alter table tablename drop primary key;
alter table tablename drop foreign key;