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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '12b96ad0ee9e891996c29d60b44a635a8e83e4ffb68c697c59421eea7fddc521' 
  AND token = 'WnJBwur1lDw9g2z0sS02TYJEc9JUalzSzmI4FZYh6BU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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