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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '511a856953e21442612c8892108a813c2a977955b137869a74de51e2eb6993b9' 
  AND token = '88GCbkRmGLsiup7AVBn7ev8aD/PA9PnlTlnbTrXppSI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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