SELECT 
  cscart_images.image_id, 
  cscart_images.image_path, 
  cscart_common_descriptions.description as alt, 
  cscart_images.image_x, 
  cscart_images.image_y 
FROM 
  cscart_images 
  LEFT JOIN cscart_common_descriptions ON cscart_common_descriptions.object_id = cscart_images.image_id 
  AND cscart_common_descriptions.object_holder = 'images' 
  AND cscart_common_descriptions.lang_code = 'en' 
WHERE 
  cscart_images.image_id = 146852

Query time 0.00058

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.00"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_images",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "image_id"
          ],
          "key_length": "4",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "792"
          },
          "used_columns": [
            "image_id",
            "image_path",
            "image_x",
            "image_y"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_common_descriptions",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "object_id",
            "lang_code",
            "object_holder"
          ],
          "key_length": "108",
          "ref": [
            "const",
            "const",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "608"
          },
          "used_columns": [
            "object_id",
            "description",
            "lang_code",
            "object_holder"
          ]
        }
      }
    ]
  }
}