[mysql] How to change the foreign key referential action? (behavior)

I have set up a table that contains a column with a foreign key, set to ON DELETE CASCADE (delete child when parent is deleted)

What would the SQL command be to change this to ON DELETE RESTRICT? (can't delete parent if it has children)

You can do this in one query if you're willing to change its name:

ALTER TABLE table_name
  DROP FOREIGN KEY `fk_name`,
  ADD CONSTRAINT `fk_name2` FOREIGN KEY (`remote_id`)
    REFERENCES `other_table` (`id`)
    ON DELETE CASCADE;

This is useful to minimize downtime if you have a large table.

Remember that MySQL keeps a simple index on a column after deleting foreign key. So, if you need to change 'references' column you should do it in 3 steps

• drop original FK
• drop an index (names as previous fk, using drop index clause)
• create new FK

ALTER TABLE DROP FOREIGN KEY fk_name;
ALTER TABLE ADD FOREIGN KEY fk_name(fk_cols)
            REFERENCES tbl_name(pk_names) ON DELETE RESTRICT;

I had a bunch of FKs to alter, so I wrote something to make the statements for me. Figured I'd share:

SELECT

CONCAT('ALTER TABLE `' ,rc.TABLE_NAME,
    '` DROP FOREIGN KEY `' ,rc.CONSTRAINT_NAME,'`;')
, CONCAT('ALTER TABLE `' ,rc.TABLE_NAME,
    '` ADD CONSTRAINT `' ,rc.CONSTRAINT_NAME ,'` FOREIGN KEY (`',kcu.COLUMN_NAME,
    '`) REFERENCES `',kcu.REFERENCED_TABLE_NAME,'` (`',kcu.REFERENCED_COLUMN_NAME,'`) ON DELETE CASCADE;')

FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS rc
LEFT OUTER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu
    ON kcu.TABLE_SCHEMA = rc.CONSTRAINT_SCHEMA
    AND kcu.CONSTRAINT_NAME = rc.CONSTRAINT_NAME
WHERE DELETE_RULE = 'NO ACTION'
AND rc.CONSTRAINT_SCHEMA = 'foo'

You can simply use one query to rule them all: ALTER TABLE products DROP FOREIGN KEY oldConstraintName, ADD FOREIGN KEY (product_id, category_id) REFERENCES externalTableName (foreign_key_name, another_one_makes_composite_key) ON DELETE CASCADE ON UPDATE CASCADE