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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b51c5fa16380a544a1f16a224734112e31ba24b53e9afe4912b48efd7ac421a6' 
  AND token = 'PXbPpJCTHOVM0k95tw75JJbfPwn96DP/FpPQsrs9Wns=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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