SELECT 
  cscart_images.*, 
  cscart_images_links.*, 
  cscart_common_descriptions.description AS alt, 
  cscart_images.image_id AS images_image_id 
FROM 
  cscart_images_links 
  LEFT JOIN cscart_images ON cscart_images_links.image_id = cscart_images.image_id 
  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_links.object_type = 'product' 
  AND cscart_images_links.type = 'A' 
  AND cscart_images_links.object_id = '6868' 
ORDER BY 
  cscart_images_links.position, 
  cscart_images_links.pair_id

Query time 0.00052

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "25.33"
    },
    "ordering_operation": {
      "using_filesort": true,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_images_links",
            "access_type": "ref",
            "possible_keys": [
              "object_id",
              "idx_object_type_type_position"
            ],
            "key": "object_id",
            "used_key_parts": [
              "object_id",
              "object_type",
              "type"
            ],
            "key_length": "81",
            "ref": [
              "const",
              "const",
              "const"
            ],
            "rows_examined_per_scan": 9,
            "rows_produced_per_join": 9,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "7.64",
              "eval_cost": "0.90",
              "prefix_cost": "8.54",
              "data_read_per_join": "864"
            },
            "used_columns": [
              "pair_id",
              "object_id",
              "object_type",
              "image_id",
              "detailed_id",
              "type",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_images",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "image_id"
            ],
            "key_length": "4",
            "ref": [
              "cscart_db.cscart_images_links.image_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 9,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "7.77",
              "eval_cost": "0.90",
              "prefix_cost": "17.21",
              "data_read_per_join": "6K"
            },
            "used_columns": [
              "image_id",
              "image_path",
              "image_x",
              "image_y",
              "is_high_res"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_common_descriptions",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "object_id",
              "lang_code",
              "object_holder"
            ],
            "key_length": "107",
            "ref": [
              "cscart_db.cscart_images.image_id",
              "const",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 9,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "7.22",
              "eval_cost": "0.90",
              "prefix_cost": "25.33",
              "data_read_per_join": "5K"
            },
            "used_columns": [
              "object_id",
              "description",
              "lang_code",
              "object_holder"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_common_descriptions), (`cscart_db`.`cscart_common_descriptions`.`object_id` = `cscart_db`.`cscart_images`.`image_id`), true)"
          }
        }
      ]
    }
  }
}