如何在不删除表的情况下更改外键引用 DELETE CASCADE

Question

I have created database tables with foreign key reference ON UPDATE CASCADE ON DELETE RESTRICT . However, I set my engine MyISAM so this reference does not work. The primary key is being deleted even if it is used elsewhere as foreign key. How can I fix this issue? I tried to alter table engine to InnoDB, but even if it is set to InnoDB the foreign references does not work. Moreover, I tried to drop one empty table with foreign key reference and engine MyISAM. Then I tried to add that table, but it does not add. Most probably when I drop table foreign references remain somewhere in schemas.

My query to create table.

CREATE TABLE IF NOT EXISTS `products` (
    `productid` int(10) NOT NULL AUTO_INCREMENT PRIMARY KEY,
    `productname` varchar(255) NOT NULL,
    `productcode` varchar(255) NOT NULL,
    `producttype` varchar(255) NULL
) 
ENGINE=MyISAM DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `sales` (
    `salesid` int(10) NOT NULL AUTO_INCREMENT PRIMARY KEY
    `productid` int(10) NOT NULL,
    `quantity` int(10) NOT NULL,
    `price` int(10) NOT NULL,
    `date` datetime NOT NULL,
    CONSTRAINT `fk_sales_productid` 
    FOREIGN KEY (productid) 
    REFERENCES products(productid) ON UPDATE CASCADE ON DELETE RESTRICT
) 
ENGINE=MyISAM DEFAULT CHARSET=utf8;

These 2 tables were created with this query as MyISAM. They have data on it which i need. I run this query to change engine to InnoDB as reference on delete cascade were not working in MyISAM. 'ALTER TABLE products ENGINE=InnoDB;' 'ALTER TABLE sales ENGINE=InnoDB;' But after making them InnoDB, the reference still does not work when I delete product, related productid in sales table becomes NULL.

Answer 1

As per P.Salmon's demo queries seems valid. You probably missing something in FK references. I suggest you to export 2 tables, the examine it in editor, especially FK references part and make sure engine is InnoDB as it has row-level locking and has what is called referential integrity that involves supporting foreign keys and relationship constraints.