SELECT 
  c.* 
FROM 
  cscart_bm_containers as c 
WHERE 
  1 
  AND c.location_id = 104

Query time 0.00028

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "c",
      "access_type": "ref",
      "possible_keys": [
        "location_id",
        "location_id_company_id",
        "location_id_position_company_id"
      ],
      "key": "location_id_company_id",
      "key_length": "3",
      "used_key_parts": ["location_id"],
      "ref": ["const"],
      "rows": 3,
      "filtered": 100
    }
  }
}

Result

container_id location_id position width user_class linked_to_default status company_id
413 104 FOOTER 16 Y A 0
414 104 CONTENT 16 content-grid Y A 0
415 104 HEADER 16 Y A 0
416 104 TOP_PANEL 16 Y A 0