SELECT 
  feature_id 
FROM 
  cscart_product_features 
WHERE 
  feature_id IN (550) 
  AND feature_type = 'E'

Query time 0.00024

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_features const PRIMARY PRIMARY 3 const 1

Result

feature_id
550