explain format = 'json'

select * from city ;
select * from country;

 explain format = 'json'

-- explain
select * from city c join country cy
on c.country_id = cy.country_id 
where city_id between 1 and 10
;
{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.76"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "c",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "idx_fk_country_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "city_id"
          ],
          "key_length": "2",
          "rows_examined_per_scan": 10,
          "rows_produced_per_join": 10,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "1.26",
            "eval_cost": "1.00",
            "prefix_cost": "2.26",
            "data_read_per_join": "2K"
          },
          "used_columns": [
            "city_id",
            "city",
            "country_id",
            "last_update"
          ],
          "attached_condition": "(`c`.`city_id` between 1 and 10)"
        }
      },
      {
        "table": {
          "table_name": "cy",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "country_id"
          ],
          "key_length": "2",
          "ref": [
            "sakila.c.country_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 10,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "2.50",
            "eval_cost": "1.00",
            "prefix_cost": "5.76",
            "data_read_per_join": "2K"
          },
          "used_columns": [
            "country_id",
            "country",
            "last_update"
          ]
        }
      }
    ]
  }
}