SELECT 
  * 
FROM 
  cscart_product_options_inventory 
WHERE 
  product_id = 10138 
  AND combination_hash = '1312185745'

Query time 0.00052

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
10138 ODV-GXL-FK06-2070 1312185745 1138_21585 0.00 N 0 2776.42 38.50 0 0 0 0 123