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SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 717 
  AND lang_code = 'en'

Query time 0.00304

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	56	Using where

Result

feature_id	variant_id	value	value_int
127	5895
178	6309
128	5899
129	5902
30	130
42	6256
135	5965
136	5972
176	6260
136	5976
136	5977
136	5973
135	5968
176	6270
176	6262