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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a6401c171e6d23f3418a329044422feed893da76828ee7e10b94a7fb16677f34' 
  AND token = '5uK0XYbObuzVVbURvZ18BTeytOTUFvE3XtJN9To1F50=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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