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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b75fd3fe23fe300acd76e9a005c121cd13ab513631d6aafaa0a5044b6bcde259' 
  AND token = 'SXuhbjpDqyIOTERsCYZlwfRBt/W3+7CpsOtt6+wba2U=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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