SELECT 
  combination 
FROM 
  cscart_product_options_inventory 
WHERE 
  product_id = 9963 
  AND amount > 0 
  AND combination != ''

Query time 0.00048

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
617_15141_1170_22148_1171_22163
617_15141_1170_22148_1171_22164
617_15141_1170_22149_1171_22163
617_15141_1170_22149_1171_22164
617_15141_1170_22150_1171_22163
617_15141_1170_22150_1171_22164
617_15141_1170_22152_1171_22163
617_15141_1170_22152_1171_22164
617_15141_1170_22155_1171_22163
617_15141_1170_22155_1171_22164
617_15142_1170_22148_1171_22163
617_15142_1170_22148_1171_22164
617_15142_1170_22149_1171_22163
617_15142_1170_22149_1171_22164
617_15142_1170_22150_1171_22163
617_15142_1170_22150_1171_22164
617_15142_1170_22152_1171_22163
617_15142_1170_22152_1171_22164
617_15142_1170_22155_1171_22163
617_15142_1170_22155_1171_22164