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1CREATE TABLE IF NOT EXISTS `category` 
2( `categoryName` varchar(128)  ,
3 `subcategoryName` varchar(128) ,
4 PRIMARY KEY (`categoryName`) )
5 ENGINE=InnoDB DEFAULT CHARSET=latin1 
6     
7ALTER TABLE `category` ADD FOREIGN KEY (`subcategoryName`) 
8REFERENCES `category`(`categoryName`) ON DELETE RESTRICT ON UPDATE RESTRICT; 
9     
10INSERT INTO `category` (`categoryName`, `subcategoryName`) VALUES
11( 'Literature','Satire'),
12( 'Science','Mathematics'),
13( 'Science','Physics'); 
14     
15#1452 - Cannot add or update a child row: a foreign key constraint fails (`php_beginner_crud_level_1`.`category`, CONSTRAINT `category_ibfk_1` FOREIGN KEY (`subcategoryName`) REFERENCES `category` (`categoryName`)) 
16     
17INSERT INTO `category` (`categoryName`) VALUES
18( 'Literature'),
19( 'Mathematics'),
20( 'Programming');