Do you want to learn Synapse Data Explorer and do you want to read only one book about it? Then you should read the book by Pericles (Peri) Rocha (Li) - Learn Synapse Data Explorer. The writer Peri Rocha is a Senior Product Manager for Azure Synapse Analytics from Microsoft. He shows a great knowledge in the book around Synapse Data Explorer and the way of working with KQL in the services.
When working with Azure Data Explorer (ADX or Synapse Data Explorer (SDX)) the data is often streamed to the Kusto engine to be available almost instantly to the end user or application accessing the Kusto engine. This is really the power of the Kusto engine - but it would also be really good to have the data off loaded to a blob storage as Parqute files for other processes (ex.