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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21d45d1d727660d431d4b4625ef054e9da716dc8c4828de1740bf7aa36ee2f01' 
  AND token = '6f8lAk9ITrcZKwWFCnayEARb9YrYgN/xBizadtaD+zU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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