SELECT 
  COUNT(*) 
FROM 
  cscart_states 
WHERE 
  country_code = 'VN'

Query time 0.00017

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "11.77"
    },
    "table": {
      "table_name": "cscart_states",
      "access_type": "ref",
      "possible_keys": [
        "cs",
        "country_code"
      ],
      "key": "country_code",
      "used_key_parts": [
        "country_code"
      ],
      "key_length": "8",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 108,
      "rows_produced_per_join": 108,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "0.97",
        "eval_cost": "10.80",
        "prefix_cost": "11.77",
        "data_read_per_join": "12K"
      },
      "used_columns": [
        "country_code"
      ]
    }
  }
}