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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '12f7631957df3597267589c9961ac42c81075953d9878b17aee80568ac792257' 
  AND token = 'kaRe+k6bl1WkxMBnCA8xgBzx6moQ2zIsA9kbW22USVY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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