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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '343e708156e271be319cf906e111cf971e5c14f557b96f919c00987ce7d2a396' 
  AND token = 'FMfsSXGcrUe4xRiOWqAFLlMI9rahf1+1w94i/u3qb/U=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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