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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c6b1d4a544f4553967f5e672981ed1ed9aa29fd50deb15275b6d55717fb5fbea' 
  AND token = '6wS0hWr5uiAlfja9YtTLFANZZDOyJvxBi50BDz1LitE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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