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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '708a9bf27c86ec9c7feb0208afe2e80c7e2f2996a843623836c7b0d9a0c47873' 
  AND token = '2b/y+mQUeaT1oldKUTu7I9Gx1BJx1Hj6QJueIbvH5ro=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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