SELECT 
  thread_id, 
  type, 
  object_type, 
  object_id 
FROM 
  cscart_discussion 
WHERE 
  thread_id = 5091

Query time 0.00009

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_discussion const PRIMARY PRIMARY 3 const 1

Result

thread_id type object_type object_id
5091 D C 734