SELECT 
  combination 
FROM 
  cscart_product_options_inventory 
WHERE 
  product_id = 8295 
  AND amount > 0 
  AND combination != ''

Query time 0.00053

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_options_inventory range pc pc 770 12 Using index condition; Using where

Result

combination
1222_22801_1223_22807
1222_22801_1223_22808
1222_22802_1223_22807
1222_22802_1223_22808
1222_22802_1223_22809
1222_22803_1223_22807
1222_22803_1223_22808
1222_22803_1223_22809
1222_22804_1223_22807
1222_22804_1223_22808
1222_22805_1223_22807
1222_22805_1223_22808