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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '8175a1fab28101a56d4fb0817663913fcf37ee31560dd02f237c12d8b6df5c52' 
  AND token = '+eRpf32TRsxDhvIPhLO40aNwnie8/4z/lVFQ+FlShs4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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