SELECT 
  feature_id, 
  feature_type 
FROM 
  cscart_product_features 
WHERE 
  feature_id IN (18, 549, 548, 16)

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "9.61"
    },
    "table": {
      "table_name": "cscart_product_features",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "feature_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 4,
      "rows_produced_per_join": 4,
      "filtered": "100.00",
      "index_condition": "(`satishecarter_dec_setup_001`.`cscart_product_features`.`feature_id` in (18,549,548,16))",
      "cost_info": {
        "read_cost": "8.81",
        "eval_cost": "0.80",
        "prefix_cost": "9.61",
        "data_read_per_join": "1K"
      },
      "used_columns": [
        "feature_id",
        "feature_type"
      ]
    }
  }
}