SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    31971, 31966, 31967, 31968, 31969, 31970, 
    31872, 31972, 31973, 31974, 31975, 
    31976, 31977, 31978, 31979, 31980, 
    31981, 31982, 31983, 31984, 31985, 
    31986, 31987, 31988, 31989
  ) 
  AND feature_id IN (23249, 23250) 
  AND lang_code = 'vi'

Query time 0.00581

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "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",
          "key_length": "12",
          "used_key_parts": ["product_id", "feature_id", "lang_code"],
          "rows": 50,
          "filtered": 100,
          "attached_condition": "cscart_product_features_values.product_id in (31971,31966,31967,31968,31969,31970,31872,31972,31973,31974,31975,31976,31977,31978,31979,31980,31981,31982,31983,31984,31985,31986,31987,31988,31989) and cscart_product_features_values.feature_id in (23249,23250) and cscart_product_features_values.lang_code = 'vi'",
          "using_index": true
        }
      }
    ]
  }
}