foreign key relationship is not working in mysql - mysql

Question

Here I am doing foreign key relation for my SQL, I am having 3 tables
product
gallery
offer
Here product table is a master table and gallery, offer tables are child table, now I trying to delete the master table entry but it not happening I am getting an error like
Cannot delete or update a parent row: a foreign key constraint fails
CREATE TABLE `product` (
`productId` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(100) COLLATE utf16_bin NOT NULL,
`price` decimal(10,0) NOT NULL,
`regOn` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`productId`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf16 COLLATE=utf16_bin
CREATE TABLE `offer` (
`offerId` int(11) NOT NULL AUTO_INCREMENT,
`productId` int(11) NOT NULL,
`offerpercentage` text COLLATE utf16_bin NOT NULL,
PRIMARY KEY (`offerId`),
KEY `productId` (`productId`),
CONSTRAINT `offer_ibfk_1` FOREIGN KEY (`productId`) REFERENCES `product` (`productId`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf16 COLLATE=utf16_bin
CREATE TABLE `gallery` (
`galleryId` int(11) NOT NULL AUTO_INCREMENT,
`productId` int(11) NOT NULL,
`galleryName` text COLLATE utf16_bin NOT NULL,
PRIMARY KEY (`galleryId`),
KEY `productId` (`productId`),
CONSTRAINT `gallery_ibfk_1` FOREIGN KEY (`productId`) REFERENCES `product` (`productId`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf16 COLLATE=utf16_bin
Expected output
Suppose I am deleting master table entry means i have to delete all child tables entry also

Answer 1

You need to apply the ON DELETE CASCADE to your foreign key references.
CREATE TABLE `product` (
`productId` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(100) COLLATE utf16_bin NOT NULL,
`price` decimal(10,0) NOT NULL,
`regOn` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`productId`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf16 COLLATE=utf16_bin
CREATE TABLE `offer` (
`offerId` int(11) NOT NULL AUTO_INCREMENT,
`productId` int(11) NOT NULL,
`offerpercentage` text COLLATE utf16_bin NOT NULL,
PRIMARY KEY (`offerId`),
KEY `productId` (`productId`),
CONSTRAINT `offer_ibfk_1` FOREIGN KEY (`productId`) REFERENCES `product` (`productId`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf16 COLLATE=utf16_bin
CREATE TABLE `gallery` (
`galleryId` int(11) NOT NULL AUTO_INCREMENT,
`productId` int(11) NOT NULL,
`galleryName` text COLLATE utf16_bin NOT NULL,
PRIMARY KEY (`galleryId`),
KEY `productId` (`productId`),
CONSTRAINT `gallery_ibfk_1` FOREIGN KEY (`productId`) REFERENCES `product` (`productId`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf16 COLLATE=utf16_bin
This tells MySQL that when the parent is deleted, delete the referencing child.