SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    48986, 48873, 48987, 48988, 48989, 48990, 
    48991
  ) 
  AND feature_id IN (24978) 
  AND lang_code = 'vi'

Query time 0.00956

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": "PRIMARY",
          "key_length": "6",
          "used_key_parts": ["feature_id", "product_id"],
          "rows": 14,
          "filtered": 0.009490067,
          "attached_condition": "cscart_product_features_values.feature_id = 24978 and cscart_product_features_values.product_id in (48986,48873,48987,48988,48989,48990,48991) and cscart_product_features_values.lang_code = 'vi'",
          "using_index": true
        }
      }
    ]
  }
}