Duplicate key name on property of a table being created on MariaDB

I just want to create a new table on my database, but doing so:

CREATE TABLE `houses` (
  `id`         int(11)      NOT NULL AUTO_INCREMENT,
  `room_id`    int(11)      NOT NULL,
  `car_id`     int(11)      NOT NULL UNIQUE,
  `name`       varchar(128) NOT NULL,
  `is_deleted` tinyint(1)            DEFAULT 0,
  `sell_at`    datetime         NULL DEFAULT NULL,
  `created_at` datetime     NOT NULL DEFAULT current_timestamp(),
  `updated_at` datetime     NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(),
  PRIMARY KEY   (`id`),
  KEY `room_id` (`room_id`),
  KEY `car_id`  (`car_id`),
  CONSTRAINT `houses_ibfk_1`
    FOREIGN KEY (`room_id`)
    REFERENCES `rooms` (`id`),
  CONSTRAINT `houses_ibfk_2`
    FOREIGN KEY (`car_id`)
    REFERENCES `cars` (`id`)
      ON DELETE CASCADE
      ON UPDATE NO ACTION
);

Return me the error:

ERROR 1061 (42000): Duplicate key name 'car_id'

I don't have any car_id elsewhere, even in this:

SELECT (
  table_schema, table_name, constraint_name
) FROM information_schema.table_constraints
WHERE table_schema
ORDER by table_schema, table_name;

What am I doing wrong ? is it because of the car_id's UNIQUE property ? it works without, but I want to be sure each houses's car is unique (no other house will use them).

And each houses's owner will have a cars when buying (creating) their house.

Solution

The error is because the definition has:

KEY `car_id` (`car_id`),

Which, by itself, is not a problem, but with the UNIQUE keyword applied to the column, the table will be created with:

UNIQUE KEY `car_id` (`car_id`)

... so the car_id becomes a duplicated KEY reference when both are present.

Simply remove the:

KEY `car_id` (`car_id`),

from the create definition, and it will work as expected.

See this dbfiddle with the part to remove commented-out. That includes an example error reusing a car's id, plus the output of the created table definition too.