SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 9871 
  AND lang_code = 'en'

Query time 0.00040

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_features_values ref lang_code,product_id,product_id_idx,product_feature_idx product_id 3 const 44 Using where

Result

feature_id variant_id value value_int
30 128
23 6273
21 95
42 145
22 98
24 107
129 5902
128 5899
127 5895
20 6052 1.300
19 93 1.100
178 6306