SQL Error 1022: Can't write; duplicate key in table
<p>I've read all the similar errors here, still can't figure out why am I getting this error</p>

<pre><code>Executing SQL script in server
ERROR: Error 1022: Can't write; duplicate key in table 'storage'
SQL Code:
    -- -----------------------------------------------------
    -- Table `storehouse`.`storage`
    -- -----------------------------------------------------
    CREATE TABLE IF NOT EXISTS `storehouse`.`storage` (
      `product_id` INT NOT NULL,
      `quantity` INT NULL,
      `storage_room` INT NULL,
      UNIQUE INDEX `product_id_UNIQUE` (`product_id` ASC),
      INDEX `storage_room_idx` (`storage_room` ASC),
      CONSTRAINT `product_id`
        FOREIGN KEY (`product_id`)
        REFERENCES `storehouse`.`product` (`product_id`)
        ON DELETE NO ACTION
        ON UPDATE NO ACTION,
      CONSTRAINT `storage_room`
        FOREIGN KEY (`storage_room`)
        REFERENCES `storehouse`.`space` (`space_id`)
        ON DELETE NO ACTION
        ON UPDATE NO ACTION)
    ENGINE = InnoDB
</code></pre>

<p>I've checked: all the keys are unique</p>