SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 10104 
  AND lang_code = 'de'

Query time 0.00056

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 74 Using where

Result

feature_id variant_id value value_int
176 6270
176 6271
127 5895
135 5963
135 5968
136 5976
42 6252
24 107
30 128
128 5899
129 5903
48 0 1.000
135 5967
135 5966
136 5972
136 5977
176 6260
135 5964
178 6306
176 6262