SELECT 
  combination 
FROM 
  cscart_product_options_inventory 
WHERE 
  product_id = 10713 
  AND amount > 0 
  AND combination != ''

Query time 0.00215

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_options_inventory range pc pc 770 2039 Using index condition; Using where

Result

combination
1307_23775_560_14378_719_15932
1307_23775_560_14378_719_15933
1307_23775_560_14379_719_15932
1307_23775_560_14379_719_15933
1307_23775_560_14381_719_15933
1307_23775_560_14382_719_15932
1307_23775_560_14382_719_15933
1307_23775_560_14383_719_15933
1307_23775_560_14384_719_15932
1307_23775_560_14384_719_15933
1307_23775_560_14385_719_15932
1307_23775_560_14385_719_15933
1307_23775_560_14386_719_15932
1307_23775_560_14386_719_15933
1307_23775_560_14387_719_15933
1307_23775_560_14390_719_15932
1307_23775_560_14390_719_15933
1307_23775_560_14391_719_15932
1307_23775_560_14391_719_15933
1307_23775_560_14393_719_15932
1307_23775_560_14393_719_15933
1307_23775_560_14394_719_15932
1307_23775_560_14394_719_15933