SELECT 
  * 
FROM 
  cscart_product_options_inventory 
WHERE 
  product_id = 381 
  AND combination_hash = '3676838241'

Query time 0.00082

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_options_inventory const PRIMARY,pc PRIMARY 4 const 1

Result

product_id product_code combination_hash combination amount temp position price weight min_qty max_qty qty_step list_qty_count aval_status
381 ODV-VLT-025-1000 3676838241 221_6760 6.00 N 25 408.94 20.00 0 0 0 0 2