SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 514 
  AND lang_code = 'en'

Query time 0.00038

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 58 Using where

Result

feature_id variant_id value value_int
178 6309
127 5895
128 5899
129 5902
30 130
176 6266
42 6251
135 5968
176 6260
135 5963
135 5967
176 6262
176 6270
176 6271
176 6259