SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 8313 
  AND lang_code = 'en'

Query time 0.00039

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 55 Using where

Result

feature_id variant_id value value_int
148 6070
32 0 599.000
41 0 249.000
30 5773
28 5776 2.800
127 5895
128 5899
129 5904
147 6066
148 6073
148 6071
148 6069
148 6075
117 5872 0.140
178 6328