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SELECT 
  object_id, 
  thread_id, 
  type, 
  object_type, 
  company_id 
FROM 
  cscart_discussion 
WHERE 
  1 
  AND object_id = 28 
  AND object_type = 'A' 
  AND cscart_discussion.company_id = 1

Query time 0.00399

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}