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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '68ce7f75436292ed5a34148451e7f1a8db8796e0d6673bb1bad538a6c7ce56df' 
  AND token = '6bRg2aEsk9reXLQjLhoR9REjqirzNjyizela4lZNfFU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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