clientRequestToken

A unique case-sensitive string used to ensure the request to create the query is idempotent (executes only once). If another StartQueryExecution request is received, the same response is returned and another query is not created. An error is returned if a parameter, such as QueryString, has changed. A call to StartQueryExecution that uses a previous client request token returns the same QueryExecutionId even if the requester doesn't have permission on the tables specified in QueryString.

This token is listed as not required because Amazon Web Services SDKs (for example the Amazon Web Services SDK for Java) auto-generate the token for users. If you are not using the Amazon Web Services SDK or the Amazon Web Services CLI, you must provide this token or the action will fail.