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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '15b674a40baa70a66c4537239cae62f00801daa1a59a26545935d9438a6a0375' 
  AND token = 'UIKJ4C7oApqo1CpE2YMf+pEL1GLmMPBbj9mJLOEMbdQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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