外键无法添加

Question

I am try to add foreign key

CREATE TABLE `uniform_product_details` ( 
  `upc_id` VARCHAR(32) NOT NULL, 
  `product_id` int(11),
  `condition_id` tinyint(1) NOT NULL,
  `status`  INT NOT NULL,
  `created_by` VARCHAR(32), 
  `updated_by` VARCHAR(32),
  `date_added` datetime NOT NULL,
  `date_modified` datetime NOT NULL,
  PRIMARY KEY(`upc_id`),
  INDEX `pid` (`product_id`),
  FOREIGN KEY(`product_id`) REFERENCES product(`product_id`) ON DELETE CASCADE
);

but my Toad showing an error while doing this

MySQL Database Error: Cannot add foreign key constraint

Is there any logical mistake I am caring with this Query. Help !!

Answer 1

Try following code:

CREATE TABLE `uniform_product_details1` ( 
  `upc_id` VARCHAR(32) NOT NULL, 
  `product_id` int(11),
  `condition_id` tinyint(1) NOT NULL,
  `status`  INT NOT NULL,
  `created_by` VARCHAR(32), 
  `updated_by` VARCHAR(32),
  `date_added` datetime NOT NULL,
  `date_modified` datetime NOT NULL,
  PRIMARY KEY(`upc_id`),
  INDEX `pid` (`product_id`),
  FOREIGN KEY(`product_id`)  REFERENCES product(`product_id`) ON DELETE CASCADE
)ENGINE=InnoDB;

Answer 2

Maybe it has to do with the Engine... MyISAM tables do not support foreign keys. Define the engine as InnoDB:

create table uniform_product_details(
    -- All your column definitions
)ENGINE=InnoDB;

You may need to change the engine for other tables. If that's the case, use this:

alter table another_table ENGINE=InnoDB;

The full sequence of the solution might be as follows:

1. Create the tables without foreign key definitions
2. Alter all your tables: Set the engine to InnoDB for all of them
3. Add the foreign key definitions with:

   alter table any_table add foreign key ... ;

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Further reference about MySQL Storage Engines:

• MySQL Reference Manual: Storage engines