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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '642eceb355721577145263e736fa098e3c29ce36a6811b9141c6f2769fd16398' 
  AND token = '16gp7AIVGz2JUPvcu7dYU7kaI1UdbIBm41OW/amvjEc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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