Sql execution error #1005 .response from the database

[giri giri]

Hello,

I am getting "SQL execution error #1005.Response from the database" error no 121 error when i execute the below sql scripts.

The foreign key named "fk_category_id" exists in both subcategory table and property table .The error is getting resolved when i name the foreign keys in these 2 tables differently .

So my question is should the foreign key names across tables be unique in mysql ??

is there any other reason that this error can occur??

CREATE TABLE IF NOT EXISTS `sampledb`.`category` (
`category_id` INT NOT NULL ,
PRIMARY KEY (`category_id`) )

CREATE TABLE IF NOT EXISTS `sampledb`.`subcategory` (
`subcategory_id` INT NOT NULL ,
`category_id` INT NULL ,
PRIMARY KEY (`subcategory_id`) ,
CONSTRAINT `fk_category_id`
FOREIGN KEY (`category_id` )
REFERENCES `realtydb`.`category` (`category_id` ))


CREATE TABLE IF NOT EXISTS `sampledb`.`property` (
`property_id` INT NOT NULL ,
`category_id` INT NULL ,
PRIMARY KEY (`property_id`) ,
CONSTRAINT `fk_category_id`
FOREIGN KEY (`category_id` )
REFERENCES `realtydb`.`category` (`category_id` ))