SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    10943, 10944, 10945, 10946, 10947, 10948, 
    10949, 10950, 10951, 10952, 10953, 
    10954, 10955, 10956, 10957, 10958, 
    10959, 10960, 10961, 10962, 10963, 
    10964
  ) 
  AND feature_id IN (553, 624, 623) 
  AND lang_code = 'en'

Query time 0.00257

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "15.37"
    },
    "table": {
      "table_name": "cscart_product_features_values",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "fl",
        "lang_code",
        "product_id",
        "fpl",
        "idx_product_feature_variant_id"
      ],
      "key": "idx_product_feature_variant_id",
      "used_key_parts": [
        "product_id",
        "feature_id",
        "lang_code"
      ],
      "key_length": "12",
      "rows_examined_per_scan": 66,
      "rows_produced_per_join": 66,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "8.77",
        "eval_cost": "6.60",
        "prefix_cost": "15.37",
        "data_read_per_join": "51K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`gaseus`.`cscart_product_features_values`.`product_id` in (10943,10944,10945,10946,10947,10948,10949,10950,10951,10952,10953,10954,10955,10956,10957,10958,10959,10960,10961,10962,10963,10964)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (553,624,623)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}