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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '243a8c511b2072a4261ff7da4cd737e4085aa73ea3baa3bb416690aea536af33' 
  AND token = 'jT1DC0XMFEUlTcyCjfEfrV9KN49BICmIRjh9udXDCBo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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