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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '138e753e017839bf57faf73bf7c1ce452be3b851d28fd7fc46e03a40afa7b55a' 
  AND token = 'k8hU6whjt40xcueoyfrF6BlVRfO+pZXCitjvXS0ujMs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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