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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21bbfa5fc42e977fd6033ff56f7237cedef173299a68e2b605dec05303d05f43' 
  AND token = '4iBVS2v4X96RIicxbTsqgmSz2eMGa5QDBFGJIQf0PfY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00042

JSON explain

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